Abstract
The zebrafish model has become one of the best research systems for high throughput drug screening. The importance of zebrafish model in human disease research and for drug discovery and development is well-recognized in the past decade. To understand the pathogenesis of infectious and inflammatory diseases, many zebrafish disease models were established, including bacterial or viral infection diseases, autoimmune encephalomyelitis and colitis. Some of the models have been applied for drug screening to evaluate the therapeutic effect of novel compounds. Besides, the zebrafish model can be integrated with image-based assays, which can transform into an automated drug-evaluating platform. Such integration of disease model and screening platform can greatly advance our understanding of immunity-related pathogenesis and to improve the drug development. By applying histological, gene expression and survival assays, we are the first group to establish a fungal infection model with zebrafish to investigate Candida albicans’ virulence, especially its hyphal formation during infection. We demonstrated that C. albicans could colonize and invade zebrafish at multiple anatomical sites and kill the fish in a dose-dependent manner. Moreover, using zebrafish embryos, we monitored C. albicans infection and visualized the interaction between pathogen and host myelomonocytic cells in vivo. Inside zebrafish, we observed the progression of the C. albicans yeast-to-hypha transition by tracking morphogenesis, and we monitored the corresponding genes expression of the pathogen. We then performed time-lapse microarray study to analyze the genes expression patterns in fungal pathogen and zebrafish host simultaneously for systems biology approach analysis, which the abovementioned is the first part of this thesis. There are two parts in my thesis and the second part is to present how we modified a published protocol to induce inflammatory bowel diseases (IBD) in zebrafish larva by incubating fish in 2,4,6-trinitrobenzenesulfonic acid (TNBS) contained solution and apply the protocol for drug screening to select immunomodulatory molecules. By incorporating IBD scoring system and genes expression assays, we selected effective candidates from tryptophan metabolites in the activation of aryl hydrocarbon receptor (AhR) signaling to protect fish from IBD and we found the uremic toxic, indoxyl sulfate (IS), possess a physiological function to promote the expression of interleukin 22 to protect fish gut from IBD instead to damaging the physiological homeostasis. This finding proposed the IS can play a role to maintain the immunological balance, which is other than what had been reported as a toxic molecules. In conclusion, our findings have expanded the application of zebrafish model to study fungal infection. We also proposed a straightforward way to evaluate novel immunomodulation chemicals for their effects in controlling inflammation in gut. With application of automated robotic platform, we expect to make significant progress in understanding pathogenesis of more infectious and inflammatory diseases, and to develop novel therapy for related patients.