Lung Epithelial Derived SPLUNC1 Regulates Th2 inflammation in Allergic Asthma

RATIONALE: Short palate, lung and nasal epithelium clone 1 (SPLUNC1) is the most abundant protein in airway epithelia and is present at high levels in normal airway surface liquid (ASL). SPLUNC1 is a multi­functional protein, which regulates ion channel, has antimicrobial activity and affects surface tension. Our previous studies demonstrate SPLUNC1 is diminished in sputum from asthmatic patients airway, which causes airway hyperresponsiveness. We hypothesized that SPLUNC1 deficiency contributes to of Th2-driven inflammation in asthmatic airways.

METHODS: Wildtype (WT) and SPLUNC1 knockout (KO) mice were intranasally challenged with house dust mite (HDM) extract or PBS on day 1, day 7 and day 14. 24 hours after last challenge, mice were euthanized airway inflammatory changes were evaluated by H&E and AB-PAS staining. Bronchoalveolar lavage (BAL) cellularity was examined using cytospin, followed by Diff-Quick staining. Cytokine levels in lung homogenate were analyzed by ELISA. SPLUNC1 protein degradation was determined by incubating human recombinant SPLUNC1/ASL from human airway epithelial cultures with HDM at different times/doses followed by immunoblotting using an antibody against SPLUNC1.

RESULTS: SPLUNC1 KO mice are more susceptible to HDM-induced airway inflammation than WT mice, and exhibit prominent Th2 phenotypes. HDM cleaves SPLUNC1 in dose and time dependent manner.

CONCLUSIONS: SPLUNC1 is an epithelial­derived factor that plays a major role in dampening Th2 inflammation in airways, which is deranged in asthma patients. SPLUNC1 deficiency is partially due to its degradation by HDM. Identifying strategies to increase SPLUNC1 resistance to HDM proteolytic activities or SPLUNC1 in ASL may lead to novel therapies to treat allergic asthma.