Up-regulation of Fas and Fas ligand and excessive apoptosis of bronchiolar and alveolar epithelial cells were identified in bleomycin-induced pulmonary fibrosis in mice. This study hypothesized that apoptosis-regulatory genes other than Fas-Fas ligand, such as p53, p21 (Waf1/Cip1), bcl-2, bcl-x, and bax, may also participate in epithelial cell apoptosis in this model. The expression of these genes was assessed by reverse transcription polymerase chain reaction (RT-PCR), RT in situ PCR, or immunohistochemistry. The expression of p53 and p21 mRNA was concurrently up-regulated in the alveolar epithelial cells at 1 h to 7 days after intratracheal instillation of bleomycin. The expression of bcl-2 mRNA was weakly up-regulated at 1 h to 14 days, while the expression level of bcl-2 protein was not changed. The expression of bcl-x(L) and bax mRNA was strongly up-regulated at 1 h to 7 days. The expression of bcl-x protein was up-regulated in lymphocytes and macrophages, whereas bax protein was up-regulated in both epithelial and inflammatory cells. It is concluded that epithelial cell apoptosis in this model may also be induced by the up-regulation of p53 and bax and by the imbalance between apoptosis-inducible and -inhibitory genes, in addition to the up-regulation of the Fas-Fas ligand pathway.
Copyright 2000 John Wiley & Sons, Ltd.