Poster abstracts
Poster number 4 submitted by Rory Chia-Ching Chien
Mechanism of Action of An in vivo Virulence Factor of Ehrlichia
Rory C. Chien (Molecular Cellular and Developmental Biology MCDB ), Mingqun Lin (Department of Veterinary Biosciences, College of Veterinary Medicine ), Yasuko Rikihisa (Department of Veterinary Biosciences, College of Veterinary Medicine )
Abstract:
Infection with Ehrlichia species, blood-borne obligate intracellular bacteria, potentially causes life-threatening diseases collectively called “Ehrlichiosis” such as human monocytic ehrlichiosis (HME). To overcome the complex mammalian immune system, establish infection, and cause diseases within the host, Ehrlichia needs to utilize additional strategies (e.g. in vivo virulence factors) to those required to infect eukaryotic cells in culture. Our laboratory developed a mouse model of ehrlichiosis using Ehrlichia japonica (Eja) which causes overwhelming infection and fatal disease in mice. We created a library of Eja mutants by using Himar1 transposon mutagenesis system that randomly inserts transposon into the Eja genome. Using this mutant library, we found that EHF0962 is required for fatal infection in mice but is dispensable for infection of cultured cell lines such as canine macrophages (DH82), monkey endothelial cells (RF/6A), and tick embryo-derived cells (ISE6). EHF0962 encodes a unique hypothetical protein EHF0962 (~13.5 kDa) that is conserved among Ehrlichia spp. We have cloned EHF0962 and obtained the recombinant EHF0962 protein and the protein-specific antiserum. We verified the presence of native EHF0962 protein in wild-type (WT) Eja and the absence of this protein in the mutant H59 that has an Himar1 insertion in EHF0962. EHF0962 mRNA is highly upregulated immediately prior to the exponential growth of WT Eja. Obligatory intracellular bacteria have a short extracellular stage in order to spread infection. Compared to WT Eja, H59 rapidly lost infectivity at the extracellular stage. Thus, our hypothesis is that EHF0962 mediates Ehrlichia resistance at the extracellular stage. To test this, we aim to investigate mechanisms by which EHF0962 confers extracellular resistance. We also aim to test whether the infectivity loss of H59 can be restored by EHF0962 molecular complementation and whether WT Eja infection can be blocked by targeting EHF0962. The results will provide critical knowledge of treating and preventing severe ehrlichiosis.
References:
Bekebrede H, Lin M, Teymournejad O, Rikihisa Y. Discovery of in vivo Virulence Genes of Obligatory Intracellular Bacteria by Random Mutagenesis. Front Cell Infect Microbiol. 2020 Feb 4;10:2.
Lin M, Xiong Q, Chung M, Daugherty SC, Nagaraj S, Sengamalay N, Ott S, Godinez A, Tallon LJ, Sadzewicz L, Fraser C, Dunning Hotopp JC, Rikihisa Y. Comparative Analysis of Genome of Ehrlichia sp. HF, a Model Bacterium to Study Fatal Human Ehrlichiosis. BMC Genomics. 2021 Jan 6;22(1):11.
Rikihisa Y. The "Biological Weapons" of Ehrlichia chaffeensis: Novel Molecules and Mechanisms to Subjugate Host Cells. Front Cell Infect Microbiol. 2022 Jan 14;11:830180.
Keywords: Human monocytic ehrlichiosis , Virulence factor , Mouse model