Abstract
The black-legged tick Ixodes scapularis transmits the human anaplasmosis agent, Anaplasma phagocytophilum. In this study, we show that A. phagocytophilum specifically up-regulates I. scapularis organic anion transporting polypeptide, isoatp4056 and kynurenine amino transferase (kat), a gene involved in the production of tryptophan metabolite xanthurenic acid (XA), for its survival in ticks. RNAi analysis revealed that knockdown of isoatp4056 expression had no effect on A. phagocytophilum acquisition from the murine host but affected the bacterial survival in tick cells. Knockdown of the expression of kat mRNA alone or in combination with isoatp4056 mRNA significantly affected A. phagocytophilum survival and isoatp4056 expression in tick cells. Exogenous addition of XA induces isoatp4056 expression and A. phagocytophilum burden in both tick salivary glands and tick cells. Electrophoretic mobility shift assays provide further evidence that A. phagocytophilum and XA influences isoatp4056 expression. Collectively, this study provides important novel information in understanding the interplay between molecular pathways manipulated by a rickettsial pathogen to survive in its arthropod vector.
Highlights
Human anaplasmosis caused by an obligate intracellular pathogen, Anaplasma phagocytophilum, is one of the most common arthropod-borne diseases in the United States, Europe and Asia[1,2,3]
Expression of isoatp4056 (Fig. 1D) and isoatp5621 (Fig. 1I) was significantly (P < 0.05) upregulated in the presence of A. phagocytophilum in comparison to the uninfected controls. These results show that A. phagocytophilum induces expression of specific tick organic anion transporting polypeptides (OATPs) in unfed ticks
Quantitative Real-time PCR (QRT-PCR) analysis revealed significant (P < 0.05) reduction of bacterial burden in both groups of A. phagocytophilum-infected tick cells treated with kat-dsRNA alone (Fig. 5E) or in combination with isoatp4056-dsRNA (Fig. 5F). These results suggest that the interplay between kynurenine aminotransferase (KAT) and IsOATP4056 pathways is critical for A. phagocytophilum survival and colonization in tick cells
Summary
Human anaplasmosis caused by an obligate intracellular pathogen, Anaplasma phagocytophilum, is one of the most common arthropod-borne diseases in the United States, Europe and Asia[1,2,3]. Understanding survival strategies of A. phagocytophilum in arthropod unfed stages would reveal important insights on the mechanism(s) on how this bacterium could persist during tick molting phases. Human organic anion and cation transporters are classified into organic anion transporting polypeptides (OATPs), organic anion transporters (OATs) and organic cation transporters (OCTs)[27] These families of proteins are highly conserved molecules among various vertebrates that play important roles in the influx of several metabolites including xanthurenic acid (XA), a metabolite from the tryptophan oxidation pathway[27,28,29,30]. Using A. phagocytophilum-I. scapularis as a model, we provide evidence to show that tick-borne pathogens modulate these highly conserved molecules and the tryptophan metabolism pathway for its survival in the medically important arthropod vector
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