Author ORCID Identifier

0000-0001-5758-9619

Date of Graduation

12-2018

Document Type

Dissertation (PhD)

Program Affiliation

Biochemistry and Molecular Biology

Degree Name

Doctor of Philosophy (PhD)

Advisor/Committee Chair

Danielle Garsin

Committee Member

Ambro van Hoof

Committee Member

Swathi Arur

Committee Member

Hung Ton-that

Committee Member

Kevin Morano

Abstract

Heme-containing peroxidases are important components of innate immunity. Many of them functionally associate with NADPH oxidase (NOX)/dual oxidase (DUOX) enzymes by using the hydrogen peroxide they generate in downstream reactions. In Caenorhabditis elegans, a ShkT-containing peroxidase, SKPO-1, and the dual oxidase, BLI-3, contribute to resistance against the human pathogen Enterococcus faecalis, likely functioning in conjunction with each other. However, the exact mechanism(s) by which peroxidases and NOX/DUOXs contribute to pathogen resistance remain unclear. Here, we demonstrated that another peroxidase, HPX-2 (Heme-PeroXidase 2), is required for resistance against some, but not all pathogens. Tissue specific RNA interference (RNAi) revealed that HPX-2 functionally localizes to the hypodermis of the worm. In congruence with this observation, hpx-2 mutant animals possessed a slightly weaker cuticle structure, indicated by higher permeability to a DNA dye, but exhibited no obvious morphological defects. In addition, fluorescent labeling of HPX-2 revealed its expression in the pharynx, an organ in which BLI-3 also resides. Interestingly, loss of HPX-2 increased intestinal colonization of E. faecalis, suggesting its role in the pharynx may limit intestinal colonization. Moreover, disruption of a catalytic residue in the peroxidase domain of HPX-2 resulted in decreased survival on E. faecalis, indicating its peroxidase activity is required for pathogen resistance. Finally, RNA-seq analysis of an hpx-2 mutant revealed changes in genes encoding for cuticle structural components under the non-pathogenic conditions. Under pathogenic conditions, genes involved in infection response were differentially regulated to a greater degree, likely due to the increased microbial burden. In conclusion, the characterization of the heme-peroxidase, HPX-2, revealed that it contributes to C. elegans pathogen resistance through a role in generating cuticle material in the hypodermis and pharynx.

Keywords

C. elegans, heme peroxidase, immunity, pathogen

Available for download on Friday, June 14, 2019

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