APOPTOSIS AND EXPRESSION OF FAS FAS LIGAND MESSENGER-RNA IN BLEOMYCIN-INDUCED PULMONARY FIBROSIS IN MICE/

The incidence of apoptosis and the expression of Fas antigen (Fas)/Fas ligand (FasL) mRNA in bleomycin-induced pulmonary fibrosis in mice we re examined. Male ICR mice were intratracheally instilled with bleomyc in (5 U/kg of body weight). The controls were injected with sterile sa line. The animals were anesthetized and killed at 1, 6, and 12 h, and 1, 3, 5, 7, 9, and 14 days after bleomycin instillation. We assessed t he incidence of apoptosis in lung tissues by DNA fragmentation on agar ose gel electrophoresis, terminal deoxynucleotidyl transferase-mediate d dUTP biotin nick end-labeling, and electron microscopy, The expressi on of Fas and FasL mRNA was detected by reverse transcription polymera se chain reaction (RT-PCR). The localization of Fas mRNA was analyzed by in situ hybridization and that of FasL mRNA was analyzed by RT in s itu PCR. The results showed that (1) a single instillation of bleomyci n leads to the rapid appearance of apoptosis in bronchial and alveolar epithelial cells, which resolves within 1 day, and (2) apoptosis reap pears on day 7 and continues for over 14 days after bleomycin instilla tion. This was accompanied with a progression of fibrosis. Corticoster oid administration completely blocked both apoptosis and fibrosis. The expression of Fas mRNA was upregulated in the alveolar epithelial cel ls by the bleomycin instillation. FasL mRNA was also upregulated in in filtrating lymphocytes after bleomycin treatment, but not in the contr ol mice, The administration of corticosteroids suppressed the expressi on of Fas and FasL mRNA as well as apoptosis and fibrosis. Although th ese results do not show that apoptosis mediated by the Fas/FasL system is directly linked to bleomycin-induced fibrosis, we speculate that e xcessive apoptosis and the Fas/FasL system play a role in the pathogen esis of bleomycin-induced lung injury.