Project Summary/Abstract
The goal of this R01 application is to determine the mechanisms by which mitochondrial dysfunction in obese
asthma exacerbates airway inflammation. Nearly 40% of asthmatics in the U.S. are obese. Obese (vs. lean)
asthmatics experience more frequent exacerbations, poorer response to inhaled corticosteroids and worse
asthma control. There is an unmet need to study the novel pathogenesis of obese asthma. We have found
mitochondrial dysfunction in obese asthma airway epithelium, including increased respiration, glycolytic rates,
reactive oxygen species, and greater numbers of dysfunctional mitochondria. We discovered up-regulation of
Parkin (Park2) in obese asthma airway epithelium. Parkin is an E3 ubiquitin ligase that regulates mitophagy by
degrading defective mitochondria. We further observed increased levels of mitochondrial DNA (mtDNA) and
palmitic acid (PA) levels in obese asthma bronchoalveolar lavage fluid and serum samples. Moreover, type 2
cytokine IL-13, type 1 cytokine IFN-g and palmitic acid (PA, a saturated fatty acid increased in obese asthma)
increased airway epithelial Parkin levels. Parkin is essential to IL-13-mediated mtDNA release and airway
neutrophilic and eosinophilic inflammation in mice and in human airway epithelial cells. We hypothesize that
Parkin is up-regulated in obese asthma airways with dysfunctional mitochondria, which is amplified by
the type 1 or type 2 cytokine milieu, enhancing mitochondrial DNA release and exaggerating airway
inflammation. In Aim 1, we will determine the mechanisms by which Parkin is up-regulated in obese asthma by
measuring Parkin, PA, mitophagy, type 1 and type 2 cytokines, and nitric oxide (NO), and performing human
airway epithelial cell and precision-cut lung slice cultures to determine if IFN-g, IL-13 and PA increase Parkin in
part by reducing transcriptional repressor THAP11. We then test if restoring NO bioavailability reduces Parkin
activity. In Aim 2, we will determine how Parkin enhances airway mtDNA release and neutrophilic inflammation.
By using Parkin, TLR9 and STAT1 knockout human airway epithelial culture and mouse models, we will test if
excessive Parkin in a type 1 cytokine setting of obese asthma promotes mtDNA release, and amplifies
neutrophilic inflammation through the TLR9/STAT1 signaling axis. In Aim 3, we will determine the mechanisms
by which Parkin enhances airway eosinophilic inflammation. We will test if Parkin-mediated mtDNA release in a
type 2 cytokine setting amplifies STAT6 signaling and pro-eosinophilic cytokine (e.g. eotaxin) production.
Research findings from our proposed studies will likely provide several key targets (e.g. Parkin, TLR9) to treat
obese asthma, a heterogenous disease currently without specific therapies.