Submitted on October 11, 2007
Accepted on March 28, 2008
Expression of the Pro-apoptotic Protein Bax is Reduced in Bronchial Mucous Cells of Asthmatics
Kurt Schwalm1, Junko F. Stevens2, Zeyu Jiang3, Mark R. Schuyler4, Ron Schrader4, Scott H Randell5, Francis H. Y. Green6, and Yohannes Tesfaigzi1*
1 Asthma and Immunology Program, Lovelace Respiratory Research Institute, Albuquerque, New Mexico, United States
2 Applied Biosystems, Foster City, California, United States
3 Dept. of Biochemistry and Molecular Biology, University of New Mexico School of Medicine, Albuquerque, New Mexico, United States
4 Deartment of Medicine, University of New Mexico School of Medicine, Albuquerque, New Mexico, United States
5 Dept of Cell and Molecular Physiology, Univ of North Carolina, Chapel Hill, North Carolina, United States
6 Respiratory Research Group, University of Calgary, Calgary, Canada
* To whom correspondence should be addressed. E-mail: ytesfaig{at}lrri.org.
The present studies were designed to determine whether our findings in mice showing that the Bcl-2-associated protein X (Bax) plays a role in the resolution of allergen-induced mucous cell metaplasia can be applied to asthma in humans. Immunostaining of autopsy tissues from mild and severe asthmatics showed a significant reduction in the percentage of Bax-positive mucous cells compared to those from non-asthmatic controls. To exclude the possibility that post mortem changes may have affected Bax expression, Bax mRNA levels in airway epithelial cells obtained from non-smoking asthmatics were compared to non-asthmatic controls. Because the number of cells obtained by bronchial brushings is limited, we developed a robust pre-amplification procedure of cDNA prior to quantitative, real-time PCR to allow detection of 100 gene targets from limited sample size even when it was prepared from partially degraded RNA. cDNA was prepared by reverse transcription from RNA isolated from bronchial epithelial cells obtained by bronchial brushings from well-characterized subjects without lung disease and from subjects with mild asthma. Quantitative analysis showed that Bax mRNA levels were significantly reduced in samples obtained from asthma patients compared to non-asthma controls. Furthermore, Bax mRNA levels were reduced when primary airway epithelial cells from 10 individuals were treated in culture with the Th2 cytokine IL-13. These studies show that Bax expression is reduced in airway epithelial cells of even mild asthmatics and suggest that restoring Bax expression may provide a clinical approach for restoring the normal numbers of epithelial cells and reduced mucous hypersecretion in asthma.
