Mucosal barriers of the intestine and the lung offer the first line of protection in the host defence mechanisms against ingested and inhaled antigens. During the 20th century, the incidence of chronic mucosal inflammatory diseases of unknown aetiology such as inflammatory bowel disease, chronic obstructive pulmonary disease and pulmonary fibrosis has risen markedly in the Western World. This PhD project used zebrafish, Danio rerio, as a model organism to study acute and chronic mucosal inflammatory responses in the intestine and the gills induced respectively by dietary components and respiratory irritants/injury associated with human disease.
A single exposure to a diet rich in cholesterol (HCD) results in the accumulation of myeloid cells in the intestine in both zebrafish and mice. HCD-induced immune cell accumulation is dependent on NFkB activation and the microbiota and acute exposure to HCD leads to caspase-1 activation in intestinal epithelial cells. Extended HCD results in localised, inflammation-dependent, functional dysregulation. This model reveals a novel route by which dietary cholesterol can initiate intestinal inflammation.
Acute exposure to cigarette smoke and silica particles leads to an acute inflammatory response in zebrafish gills similar to that seen in mammalian lungs. Despite gill tissue remodelling following long-term exposure to these irritants, no collagen deposition, i.e. fibrosis, could be detected. When combined with severe tissue damage induced by cryoinjury, exposure to silica delayed wound-healing responses and again no fibrotic changes were observed. Preliminary gene expression analysis by RNA-seq showed altered gene expression of similar genes to those involved during wound-healing processes in mammals. These results provide a basis for further investigations such as extensive comparisons of gene expression with fibrosis in mammals.
Overall, these findings demonstrate that the zebrafish is a valuable and pathophysiologically relevant model in which to study mucosal inflammatory diseases.