Anaplasma phagocytophilum and Ehrlichia chaffeensis cause emerging potentially fatal infectious diseases human granulocytic anaplasmosis (HGA) and human monocytic ehrlichiosis (HME), respectively. These pathogens are fastidious obligatory intracellular bacteria that infect human leukocytes, and ticks are biological vectors for transmission. How these bacteria enter and continue to thrive within hostile host milieu such as neutrophils, macrophages, and the tick cells is largely unknown. Our hypothesis is bacterial Type IV secretion (T4S) system and two-component system (TCS) play important roles in this process.
The specific aims of this project are as follows: 1. Characterize T4S effector molecules, interacting host proteins, and downstream events using yeast two-hybrid system, co-immunoprecipitation, double immunofluorescence labeling, and various pharmacological signal inhibitors and inducers, and by phenotype analysis of host cells transfected with wild-typeT4S effectors or mutant effectors with appropriate modifications (truncation, amino acid substitution, etc.). 2. Characterize CtrA function by analyzing the temporal expression of CckA and CtrA during intracellular replication and development of E. chaffeensis and A. phagocytophilum in human leukocytes and tick cells, and demonstrating CtrA regulation of genes with the upstream CtrA consensus binding site. 3. Identify genes regulated by NtrX by affinity purification of genomic DNA fragments bound to the activated recombinant NtrX, sequencing the DNA fragments, and investigate the downstream events. 4. Characterize PleD function of E. chaffeensis and A. phagocytophilum by analyzing the PleC and PleD temporal expression in human leukocytes and tick cells, verifying PleD diguanyl cyclase activity and identifying c-di-GMP binding protein targets and their functions. The data to be obtained from this study will continue to provide a breakthrough to new understanding of the dynamic signaling events between obligatory intracellular bacteria and their hosts. The results may point to a potential target for treatment and prevention of HME and HGA.

Public Health Relevance

Human granulocytic anaplasmosis and human monocytic ehrlichiosis are emerging tick- borne infectious diseases. The proposed research project will investigate how anaplasma and ehrlichia pathogens sense human granulocyte, monocyte, and tick cell environment and subvert their antimicrobial defense. The knowledge may not only contribute to developing new efficacious chemotherapy, chemoprevention, and vaccine strategies for these diseases, but also may uncover common themes in obligate intracellular parasitism and vector-borne zoonotic pathogens.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
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Host Interactions with Bacterial Pathogens Study Section (HIBP)
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Perdue, Samuel S
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Ohio State University
Veterinary Sciences
Schools of Veterinary Medicine
United States
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Cheng, Zhihui; Lin, Mingqun; Rikihisa, Yasuko (2014) Ehrlichia chaffeensis proliferation begins with NtrY/NtrX and PutA/GlnA upregulation and CtrA degradation induced by proline and glutamine uptake. MBio 5:e02141
Niu, Hua; Rikihisa, Yasuko (2013) Ats-1: a novel bacterial molecule that links autophagy to bacterial nutrition. Autophagy 9:787-8
Liu, Hongyan; Bao, Weichao; Lin, Mingqun et al. (2012) Ehrlichia type IV secretion effector ECH0825 is translocated to mitochondria and curbs ROS and apoptosis by upregulating host MnSOD. Cell Microbiol 14:1037-50
Kumagai, Yumi; Matsuo, Junji; Cheng, Zhihui et al. (2011) Cyclic dimeric GMP signaling regulates intracellular aggregation, sessility, and growth of Ehrlichia chaffeensis. Infect Immun 79:3905-12
Cheng, Zhihui; Miura, Koshiro; Popov, Vsevolod L et al. (2011) Insights into the CtrA regulon in development of stress resistance in obligatory intracellular pathogen Ehrlichia chaffeensis. Mol Microbiol 82:1217-34
Rikihisa, Yasuko (2011) Mechanisms of obligatory intracellular infection with Anaplasma phagocytophilum. Clin Microbiol Rev 24:469-89
Kumagai, Yumi; Matsuo, Junji; Hayakawa, Yoshihiro et al. (2010) Cyclic di-GMP signaling regulates invasion by Ehrlichia chaffeensis of human monocytes. J Bacteriol 192:4122-33
Rikihisa, Yasuko; Lin, Mingqun (2010) Anaplasma phagocytophilum and Ehrlichia chaffeensis type IV secretion and Ank proteins. Curr Opin Microbiol 13:59-66
Rikihisa, Yasuko (2010) Molecular events involved in cellular invasion by Ehrlichia chaffeensis and Anaplasma phagocytophilum. Vet Parasitol 167:155-66
Niu, Hua; Kozjak-Pavlovic, Vera; Rudel, Thomas et al. (2010) Anaplasma phagocytophilum Ats-1 is imported into host cell mitochondria and interferes with apoptosis induction. PLoS Pathog 6:e1000774

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