Date of Award
Doctor of Philosophy (PhD)
Biomedical Sciences - Microbiology & Immunology
Vector-borne diseases (VBDs) are human illness transmitted by an arthropod vector. World Health Organization (WHO) estimates that VBD has a huge impact worldwide that is responsible for affecting a billion people and causes 700,000 deaths annually. In recent years, there has been a continuous increase in the incidences of tick-borne diseases such as Lyme diseases and human anaplasmosis as reported by Center for Disease Control and Prevention. Very few reliable VBD control strategies have emerged till now. Transmission-blocking vaccines can provide effective management of VBDs but requires identification and characterization of novel vector-pathogen conserved molecules that play a significant role in pathogen survival and transmission from the vector host. This work describes two studies identifying the role of conserved tick organic anion transporting polypeptides (OATPs) in bacterial and viral infections. In the first study, the results show that A. phagocytophilum modulates a specific tick host organic anion transporting polypeptide (isoatp4056) and kynurenine aminotransferase (kat), a gene responsible for the production of metabolite xanthurenic acid (XA) from tryptophan catabolism pathway, for its survival in Ixodes scapularis ticks. Silencing of isoatp4056 expression using RNA interference revealed that this gene has no effect on bacterial acquisition from the murine host, but affects bacterial survival in tick cells. Furthermore, silencing of gene expression for either kat alone or with isoatp4056 affected both bacterial survival and expression of isoatp4056. Exogenous addition of XA revealed increased isoatp4056 expression and bacterial burden in tick salivary gland and ticks cells. By using electrophoretic mobility shift assays (EMSA), the study provides evidence that both XA and A. phagocytophilum influences regulation of isoatp4056 gene.
The second part of the study focuses on characterization of the role of these conserved organic anion transporting polypeptides in association with Lyme disease agent Borrelia burgdorferi and tick-borne Langat virus (LGTV), a viral pathogen closely related to tick-borne encephalitis virus (TBEV). Quantitative Real-Time PCR (QRT-PCR), data show that B. burgdorferi has no impact on the arthropod oatps gene expression in unfed nymphal ticks. Similarly, synchronous LGTV infection of unfed ticks (nymphs) revealed no impact on the expression of tick OATPs. However, specific OATPs were significantly downregulated upon LGTV infection in ticks cells at 24 h but not at 72 h post infection (p.i.). Furthermore, OATP inhibitor (SPZ) treatment followed by LGTV infection of tick cells showed significant reduction of LGTV loads, expression of kat gene, and several OATP genes. Bioinformatic characterization of medically important arthropod vectors including ticks, mosquitos, and lice revealed presence of several post-translational modifications sites such as glycosylation, phosphorylation and myristoylation sites. This set of studies provides a novel understanding on the manipulation of conserved OATPs, tryptophan pathway byproduct XA and kat, by a rickettsial pathogen for its survival in the tick vector host. In addition, these studies provide evidence on the role of tick OATPs in vector-tick-borne virus interactions. Collectively, this study provides compelling evidence on the involvement of arthropod OATPs in tick interactions with intracellular bacteria and viruses.
Taank, Vikas K..
"Arthropod Organic Anion Transporting Polypeptides in Tick-Borne Bacterial and Viral Infections"
(2019). Doctor of Philosophy (PhD), Dissertation, Biological Sciences, Old Dominion University, DOI: 10.25777/1tee-8n09