The goal of this project is to determine the role of Toll-interacting protein (Tollip) in regulating lung defense against rhinovirus infection related to asthma exacerbations. Tollip has been proposed as a negative immune regulator for host defense against bacterial infections. It is widely expressed by various types of cells, including lung epithelial cells. Tollip single nucleotide polymorphisms (SNPs) have been identified, but the role of Tollip in asthma has not been investigated. We found that Tollip rs5743899 AG genotype is more frequent in asthmatics than normal controls. Importantly, asthmatics with the AG genotype demonstrate lower lung function than asthmatics with the AA genotype. Moreover, human airway epithelial cells carrying the AG genotype express less Tollip than the AA genotype. The combination of type 2 cytokine IL-13 and rhinovirus further decreases Tollip expression. Epithelial cells carrying the AG genotype demonstrate, when treated with IL-13 and rhinovirus (RV), a stronger pro-inflammatory response, but weaker anti-viral response. We therefore hypothesize that reduction of Tollip in a subset of genetically defined asthmatics, especially in the setting of type 2 inflammation and viral infection, exaggerates airway inflammation and asthma severity.
Aim 1 will determine the role of Tollip rs5743899 in asthma lung inflammation, infection and function. By using brushed human bronchial and nasal epithelial cells and bronchoalveolar lavage fluid from asthmatics and normal subjects, we will measure Tollip expression, inflammatory and anti-viral responses, and rhinovirus burden. These data along with the surfactant protein A2 (SP-A2) genetic variant data will then be correlated with asthma lung function and disease severity.
Aim 2 will determine mechanisms by which Tollip regulates inflammation and viral infection in asthma. By using primary human bronchial and nasal epithelial cell cultures, and Tollip and autophagy gene knockout mouse models of allergen exposure and rhinovirus infection, we will test the hypothesis that in a type 2 cytokine milieu, Tollip inhibits the Toll-like receptor (TLR) signaling and pro-inflammatory cytokine production, but enhances the anti-viral response via enhancing the autophagy activity.
Aim 3 will determine cooperation of Tollip and SP-A in airway defense against viral infections. By using SP-A and Tollip knockout and transgenic mouse models of allergen exposure and rhinovirus infection, we will test the hypothesis that Tollip cooperates with SP-A to inhibit airway viral infections in asthma. SP-A maintains or increases Tollip levels, which in turn further decreases airway inflammation and viral infection. Successful completion of Project 2 will deepen our understanding of airway innate immunity dysfunction in asthma. The role of Tollip in asthma is not known and may act in concert with SP-A to further modulate response to RV during asthma exacerbations. Unraveling Tollip genetic variation and function may improve our understanding of asthma heterogeneity and corresponding personalized disease management.
