Conditioned Medium from Irradiated Bovine Pulmonary Artery Endothelial Cells Stimulates Increased Protein Synthesis by Irradiated Bovine Lung Fibroblasts in Vitro

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Abstract
Pulmonary fibrosis, a potentially fatal consequence of radiation exposure, occurs by unknown mechanisms. The hypothesis that endothelial cells, injured by radiation, could alter the biochemical function of lung fibroblasts, was tested by exposing cultures of bovine pulmonary artery endothelial cells to 0 or 5 Gy radiation and then incubation them in fresh medium for 48 h. This endothelial cell conditioned medium (ECCM) was then applied to irradiated or nonirradiated cultures of bovine lung fibroblasts. Forty-eight hours later the fibroblasts were analyzed for their ability to synthesize DNA and protein. The ECCM from injured cells stimulated fibroblasts protein synthesis twofold to threefold in irradiated fibroblasts without increasing DNA synthesis. It also stimulated a significant but less marked increase in protein synthesis in nonirradiated fibroblasts. Two-dimensional gel electrophoresis revealed this increased synthesis to be expressed in less than 10% of the 1100 separable fibroblast proteins. This study shows that endothelial cells injured by radiation produce factors that stimulate injured fibroblasts to markedly increase their synthesis of certain intracellular proteins, while not stimulating fibroblast replication.