Antioxidant enzyme expression in rat lungs during hyperoxia.
Ho, Ye-Shih, Margaret S. Dey, and James D. Crapo.
Division of Pulmonary and Critical Care Medicine, Department of
Medicine, Duke University Medical Center, Durham, NC 27710
APStracts 3:0005L, 1996.
To understand the molecular mechanisms that up-regulate the activities
of pulmonary antioxidant enzymes in adult rats during exposure to 85%
oxygen, the relative contents of corresponding mRNAs in normal and
hyperoxic lungs were determined. Hyperoxic exposure drastically
induced the expression of lung manganese-containing superoxide
dismutase (MnSOD) mRNA. Maximal induction of MnSOD mRNA occurred at
days 3 and 5 of exposure to hyperoxia, reaching a 600% and a 340%
increase over the levels of air-exposed rats, respectively. In
addition, hyperoxia induced lung mRNAs for glucose-6-phosphate
dehydrogenase, glutathione peroxidase, glyceraldehyde-3-phosphate
dehydrogenase, [alpha]-tubulin, and [delta]-actin to different
extents at various days of exposure. Hyperoxia had little or no
effect on the levels of mRNAs for copper/zinc-containing superoxide
dismutase (CuZnSOD), catalase, heat shock protein, hsp70 and creatine
kinase. Nuclear run-on experiments showed that the transcriptional
rate of the MnSOD gene is enhanced in hyperoxic rat lungs by
approximately 400% at day 3 of exposure compared to that of controls.
The specific activities of CuZnSOD and MnSOD in these lung samples
per unit of lung protein or DNA were also determined. The activity of
CuZnSOD in hyperoxic lungs was found to be unchanged compared with
controls except a 20% decrease at day 7 of exposure when standardized
against protein content of lung homogenate. Changes of CuZnSOD
activity were more dramatic in hyperoxic lungs (a 40% increase at
days 3, 5, 7, and 14 of exposure) when enzyme activity was normalized
using lung DNA content. Surprisingly, no proportional increase of
lung MnSOD enzyme activity was observed at days 3 and 5 of oxygen
exposure. The increase of MnSOD activity per unit of lung protein
also did not parallel increases in MnSOD protein content at days 5, 7
and 14 of exposure. These data suggest that, in addition to
transcriptional activation, translational and/or post-translational
regulation of the MnSOD gene expression may play a critical role in
controlling lung MnSOD activity upon hyperoxic exposure.
Received 18 December 1994; accepted in final form 6 December
1995.
APS Manuscript Number L363-4.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96