Abstract
Ticks are hematophagous arthropods, and their blood feeding on vertebrate hosts is essential for their development. The vertebrate blood contains high levels of free iron that can react with oxygen in ticks, resulting in the production of hydrogen peroxide (H2O2), one of the reactive oxygen species. Peroxiredoxins (Prxs), H2O2-scavenging enzymes, take on an important role in the ticks' oxidative stress coping mechanism. Ticks also transmit several disease-causing pathogens, including tick-borne encephalitis virus (TBEV), in animals and humans. Therefore, the control of ticks and tick-borne pathogens is a key issue that needs to be addressed. Infection with an arthropod-borne flavivirus is known to induce oxidative stress in insect cells. We hypothesize that vector-derived Prxs could have an effect on the infection and/or replication of flaviviruses in the hosts, since ticks Prxs are possibly transmitted from ticks to their hosts. In this study, we established stable strains of baby hamster kidney (BHK) cells expressing two types of H2O2-scavenging Prxs from the hard tick Haemaphysalis longicornis (BHK-HlPrx and BHK-HlPrx2 cells). Although the infection of TBEV surrogate Langat virus (LGTV) did not induce H2O2 production in normal BHK cells, the mortality rate and the virus titer of LGTV infected BHK-HlPrx cells increased. In addition, HlPrx proteins in BHK cells can facilitate LGTV replication in cells, while HlPrx2 proteins in BHK cells cannot. The results also demonstrated that this facilitation of LGTV replication by the 1-Cys Prx in the BHK cells is not by scavenging H2O2 but by an unknown mechanism. In order to understand this mechanism, more studies using tick-derived cells and ticks are necessary.
Highlights
Ticks are obligate hematophagous ectoparasites and require blood feeding throughout their life cycle, except in the egg stage
Western blotting demonstrated that the FLAG-tagged HlPrx and HlPrx2 in baby hamster kidney (BHK) cells were detected with molecular weights of 25.7 kDa and 23.5 kDa, respectively (Figure 1)
In the normal BHK cells, FLAG-tagged HlPrxs were not detected. These results demonstrated that the HlPrx- or HlPrx2-expressing plasmid-transfected BHK cell lines (BHK-HlPrx and BHKHlPrx2 cells) expressed a certain Prx protein in the cells
Summary
Ticks are obligate hematophagous ectoparasites and require blood feeding throughout their life cycle, except in the egg stage. Ticks feed on vertebrate blood that contains high levels of iron, like heme, Tick Prx Facilitates LGTV Replication and ferrous iron (Galay et al, 2014). Ticks have antioxidant enzymes that scavenge H2O2, like peroxiredoxins (Prxs) (Tsuji et al, 2001; Kusakisako et al, 2016a), catalases (Kumar et al, 2016), and selenoproteins (Adamson et al, 2014). Reports have demonstrated that the knockdown of these H2O2-scavenging enzyme genes has an inhibition effect on tick blood feeding and/or reproduction (Adamson et al, 2014; Kumar et al, 2016; Kusakisako et al, 2016a). The antioxidant enzymes controlling the H2O2 concentration in ticks can be considered to be important in tick blood feeding and reproduction (Kusakisako et al, 2018a)
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