1. ¹Department of Pediatrics (Neonatology), School of Medicine and Dentistry, University of Rochester, Rochester, New York
2. ²Department of Pathology and Laboratory Medicine, School of Medicine and Dentistry, University of Rochester, Rochester, New York

Correspondence: Dr. Michael A. O'Reilly, Department of Pediatrics (Neonatology), Box 777, Children's Hospital at Strong, The University of Rochester, 601 Elmwood Avenue, Rochester, NY 14642. Fax: 716 756 7780; E-mail: michael_oreilly@urmc.rochester.edu

Received 20 July 2000.

Abstract

Exposure of the lung to severe hyperoxia induces terminal transferase dUTP end-labeling (TUNEL) indicative of DNA damage or apoptosis and increases expression of the tumor suppressor p53 and of members of the Bcl-2 gene family. Because cell survival and apoptosis are regulated, in part, by the relative abundance of proteins of the Bcl-2 family, we hypothesized that lung cells dying during exposure would show increased expression of pro-apoptotic members, such as Bax, whereas surviving cells would have increased expression 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 hyperoxia, with specific focus on correlating expression of Bax and Bcl-X_L with morphologic 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 decreased levels of Bcl-w and Bfl-1. In situ hybridization revealed that hyperoxia induced Bax and Bcl-X_L mRNA in uniform and overlapping patterns of expression throughout terminal bronchioles and parenchyma, coinciding with TUNEL staining. Electron microscopy and DNA electrophoresis, however, suggested relatively little classical apoptosis. Unexpectedly, Western analysis demonstrated 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, oxygen toxicity was not lessened by p53 deficiency. These findings suggest that oxygen-induced lung injury does not depend on the relative expression of these Bcl-2 members.