Date of Award

8-2014

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Microbiology

Advisor

Carol H. Kim

Second Committee Member

John. T Singer

Third Committee Member

Roger B. Sher

Abstract

The zebrafish (Danio rerio) has become a model organism for a number of different diseases and infection models. One of these models, bacteremia, often preludes sepsis, a serious inflammatory condition that can result in multi-organ failure and death. Bacterial infection and inflammation can cause mitochondrial dysfunction, which is characterized by aberrant mitochondrial ROS production, mtDNA damage and further activation of inflammatory and apoptotic signaling cascades. An antioxidant present in the mitochondria, SOD2, is responsible for the neutralization of these ROS. Inefficient neutralization of these mROS via loss of SOD2 would lead to exaggerated inflammation, apoptosis, and ultimately, organ failure and death. Here, we use the zebrafish model and morpholino-mediated knockdown to characterize the role of sod2 in innate immunity. We first sought to determine the spatial and temporal expression of sod2 in the developing embryo. It was revealed that sod2 was expressed in key hematopoietic regions of these embryos, preliminarily indicating to us that sod2 could play a role in myeloid cell populations. Knockdown of sod2 via morpholino resulted in increased susceptibility to Pseudomonas aeruginosa infection. Further investigation revealed that sod2 was necessary for phagocyte population maintenance. We hypothesized that phagocytes were affected by the buildup of mitochondrial superoxide, so we introduced a mitochondrial ROS scavenger to the water of sod2 morphants. We saw that neutrophil populations were restored and bacterial burden was reduced in these morphants, confirming that mitochondrial superoxide neutralization is necessary for phagocyte maintenance and therefore, an efficient innate immune response to bacteria.

The zebrafish has also been used for the study of cystic fibrosis (CF). CF is an autosomal recessive condition that is a result of the mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. As a chloride channel, CFTR is responsible for regulating the influx and efflux of chloride ion in and out of the cell. Mutations to CFTR result in either nonfunctional CFTR at the cell membrane or degradation before it reaches the cell membrane. One of the proteins responsible for the trafficking of CFTR to the cell membrane is Na+ H+ exchanger regulatory factor (NHERF1). NHERF1 is a PDZ-domain containing protein, which interacts with specific amino acid residues often found at the C-terminal end of target proteins. CFTR, along with iNOS, CXCR2, and PTEN, contain this motif that interacts with the PDZ domain of NFIERF1. Using the zebrafish model, we attempted to assess the role that NHERF1 and these interacting proteins may be playing in the innate immune response. Knockdown of nherfl demonstrated its necessity for an efficient innate immune response to P. aeruginosa. Nherfl morphants were seen to have a dampened respiratory burst response and decreased neutrophil migration, both serving as potential causes for the susceptibility to infection. As of now, though, it is unclear exactly which protein-protein interactions between Nherfl and its partners are affecting innate immunity the most. Taken together, these gene studies reveal unique roles for both Sod2 and Nherfl in the innate immune response to bacterial infection.

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