Asthma is a common disease of the large airways and the airway epithelium has a sentinel role in the initiation of the disease. Interleukin-33 is located in the nucleus of airway epithelium and is increased in asthmatic airway epithelium. Furthermore the gene has been reproducibly associated with asthma by genome wide association studies. Originally identified as a nuclear factor, interleukin-33 was found to act as a cytokine via the receptor ST2. Since this point the majority of research on interleukin-33 has focused on its role as a cytokine. Studies of its nuclear role have investigated the expression of a handful of inflammatory genes. This thesis examines the role of nuclear interleukin-33 in the airway epithelium using a functional genomics approach.
The alveolar A549 cell line and normal primary bronchial epithelial cells were found to express full-length interleukin-33 mRNA. Both were taken forward for interleukin-33 knockdown studies using enzyme-linked immunosorbent assays to measure relevant cytokines in supernatants. Upon interleukin-33 knockdown, interleukin-1ß-induced interleukin-6 and interleukin-8 secretion was reduced in both A549 and primary cells. Microarray analyses of gene expression showed interleukin-33 affected genes involved in differentiation, cell-substrate adhesion and extracellular matrix organisation. In contrast, ST2 knockdown resulted in increases in cytokine secretion upon interleukin-1ß stimulation with global gene expression analyses showing little overlap with interleukin-33-effected genes. Taken together, this suggests that the gene expression changes found upon interleukin-33 knockdown were due to a nuclear role. Finally, chromatin-immunoprecipitation sequencing was used to determine genome wide the DNA-binding sites of interleukin-33. Transcription factor binding motifs and preferential binding near promoters and exons were found but further replicates are required for confidence in these results.
This work shows that interleukin-33 has an important nuclear role that appears to regulate gene expression in a manner that could mediate the changes seen in the asthmatic lung.