VARIABLE EXPRESSION OF PLATELET-DERIVED GROWTH-FACTOR FAMILY PROTEINSIN ACUTE LUNG INJURY

During acute lung injury, there is an outpouring of growth factors int o the alveolar space that drive local repair and fibrosis. During the remodeling that follows the instillation of bleomycin via the trachea into the adult rat, at least two platelet-derived growth factor (PDGF) -like peptides are released sequentially into lung lining fluid. Group s of four to five animals were killed at 3, 6, 15, and 26 days after e xposure to bleomycin and lungs lavaged with isotonic saline. PDGF-like peptides in epithelial lining fluid (ELF) were partially purified by cation exchange chromatography and concentrated. Isolated peptides wer e analyzed by immunoblotting to determine their molecular weight and i mmunologic identity. Western blots were probed with polyclonal antibod ies to PDGF-BB and PDGF-AA. PDGF-Iike peptides of two distinct size cl asses (38-40 kD and 29 kD) were present in alveolar fluid from all rat s with lung injury induced by bleomycin. No PDGF-like peptides were fo und in comparably prepared ELF from control animals. The 38-40 kD pept ide was detected only with anti-PDGF-BB antibody; the 29 kD peptide wa s detected only with anti-PDGF-AA antibody. The presence of these two peptides varied independently with time after exposure to bleomycin. T he 38-40 kD peptide was at peak levels at 3 to 6 days. In contrast, th e 29 kD peptide was present at all times following injury but with far less variation over time. In parallel with these immunoassays for PDG F-like molecules, there was abundant growth-promoting activity for fib roblasts present in concentrated ELF during the course of injury. Bioa ssays of processed lavage fluid were used to determine the mitogenic p otency of ELF for lung fibroblasts. The amount of growth-promoting act ivity paralleled over time the amount of the 38-40 kD peptide detected on immunoblots. At day 3, the mitogenic activity of chromatographical ly purified PDGF-like peptides was equivalent in potency to 12.1 +/- 1 .6 ng/ml of authentic PDGF. Anti-PDGF antibodies blocked the activity of ELF: 64% of the activity was inhibited by anti-PDGF-BB antibodies; 15% of the activity was inhibited by antiPDGF-AA antibodies. The prese nce of several PDGF-like peptides in ELF during the evolution of tissu e repair in this model supports the notion that these important mitoge ns for mesenchymal cells are central to the remodeling process in lung .