FIBROBLASTS ISOLATED AFTER FIBROTIC LUNG INJURY INDUCE APOPTOSIS OF ALVEOLAR EPITHELIAL-CELLS IN-VITRO

Primary lung fibroblasts were isolated from patients with idiopathic p ulmonary fibrosis (HIPF), from normal human lung tissue (NH), from rat s treated with 75% oxygen and paraquat (PA), and from normal adult rat s (NR). Serum-free media conditioned by each fibroblast strain were te sted on the human A549 cell line (HIPF and NH media) or on primary alv eolar epithelial cells (AEC) isolated from normal adult rats (PA or NR media). Over 20-h incubation, HIPF- or PA-conditioned media induced D NA fragmentation and significant decreases in total recoverable DNA an d cell number of A549 or AEC, respectively; NH or NR media had no sign ificant effect relative to serum-free unconditioned media. Apoptosis o f A549 and AEC was detected by altered nuclear morphology and was conf irmed by terminal deoxynucleotidyl transferase-mediated bio-dUTP nick end labeling. The endonuclease inhibitors 10 mu M aurintricarboxylic a cid and 50 mu M zinc inhibited HIPF-induced apoptosis of A549 cells by 68 and 71%, respectively. Both apoptosis and necrosis were induced by HIPF and PA media in a concentration-dependent manner. These results suggest that altered fibroblasts emerging during fibrotic lung injury release a soluble factor(s) capable of inducing cell death and net los s of AEC.