Bcl-2 family gene expression during severe hyperoxia induced lung injury

Exposure of the lung to severe hyperoxia induces terminal transferase dUTP end-labeling (TUNEL) indicative of DNA damage or apoptosis and increases ex pression of the tumor suppressor p53 and of members of the Bcl-2 gene famil y. Because cell survival and apoptosis are regulated, in part, by the relat ive abundance of proteins of the Bcl-2 family, we hypothesized that lung ce lls dying during exposure would show increased expression of pro-apoptotic members, such as Bax, whereas surviving cells would have increased expressi on of anti-apoptotic members, such as Bcl-X-L. The hypothesis is tested in the current study by determining which Bcl-2 genes are regulated by hyperox ia, with specific focus on correlating expression of Bax and Bcl-X-L with m orphologic evidence of apoptosis or necrosis. Adult mice exposed to greater than 95% oxygen concentrations for 48 to 88 hours had increased whole-lung mRNA levels of Bax and Bcl-X-L, no change in Bak, Bad, or Bcl-2, and decre ased levels of Bcl-w and Bfl-1. In situ hybridization revealed that hyperox ia induced Bax and Bcl-X-L mRNA in uniform and overlapping patterns of expr ession throughout terminal bronchioles and parenchyma, coinciding with TUNE L staining. Electron microscopy and DNA electrophoresis, however, suggested relatively little classical apoptosis. Unexpectedly, Western analysis demo nstrated increased Bcl-X-L, but not Bax, protein in response to hyperoxia. Bax and Bfl-1 were not altered by hyperoxia in p53 null mice; however, oxyg en toxicity was not lessened by p53 deficiency. These findings suggest that oxygen-induced lung injury does not depend on the relative expression of t hese Bcl-2 members.