Resolution of Epithelial Cell Hyperplasia in Asthma

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Project Summary/Abstract During the previous funding period we elucidated the molecular mechanisms of Bik/Nbk-induced apoptosis in hyperplastic airway epithelial cells (AECs) and identified Bik-derived peptides that activate Bak and reduce mucous cell hyperplasia (MCH) in mice. While we were evaluating the effects of Bik deficiency on MCH, we noticed that among females, but not males, bik-/- compared with bik+/+ mice show enhanced inflammation in response to LPS and cigarette smoke exposure. Further, we noticed that instillation of Bik-derived peptides or transgenic expression of Bik in AECs in an inducible fashion suppressed allergen-induced inflammation. Even more striking was that IL-6 levels were increased in lung tissues of bik-/- compared with bik+/+ mice at baseline in the absence of inflammatory stimuli, and that bik-/- mice develop emphysema at 80 weeks of age. The role of Bik in regulating inflammation was confirmed by our observation that primary murine airway epithelial cells (MAECs) from female bik-/- compared with bik+/+ show increased levels of nuclear factor kappaB (NF-κB). In humans, we identified a single nucleotide polymorphism (SNP) within the BIK promoter region that is associated with decline in lung function in four independent cohorts for subjects older than 60 years of age. The AG change causes reduced BIK gene expression and females with reduced Bik levels show increased circulating IL-6 levels. Because Bik blocks baseline inflammation in naïve bik-/- mice we propose that this is the actual function of Bik rather than it's cell death inducing activity; and if left unchecked can lead to lung destruction during aging. Therefore, this renewal application is focused on elucidating the central role of Bik in blocking inflammation by reducing nuclear p65 levels. Aim 1 will determine the importance of localization of Bik and Bcl-2 at the ER for reducing inflammation at baseline in the absence of inflammatory stimuli. Mutations of functional sites within Bik and Bcl-2 proteins will show the sites of interaction between Bik, Bcl-2 and p65. Further, the possible role of increased Bcl-2 expression in female cells causing the sex-dependent differences in inflammation will be explored. Aim 2 will test the causal role of Bik deficiency on increased inflammation by restoring Bik levels using adenoviral expression of Bik or treating with the Bik-derived peptide to reduce secreted IL-6 levels in differentiated bik-/- MAECs and primary human airway epithelial cells homozygous for the G allele. Further, the causal role of Bik in the development of emphysema in aging female mice will be evaluated using transgenic inducible expression of Bik in the lungs of bik-/- mice to block baseline inflammation. These studies will lay the foundation for a precision medicine-based treatment of COPD and asthmatic bronchitis.