Identification of two forms of cyclophilin from the hard tick Haemaphysalis longicornis

Inhibitory effect of cyclophilin A from the hard tick Haemaphysalis longicornis on the growth of Babesia bovis and Babesia bigemina

Haemaphysalis longicornis is known as one of the most important ticks transmitting Babesia parasites in East Asian countries, including Babesia ovata and Babesia gibsoni, as well as Theileria parasites. H. longicornis is not the natural vector of Babesia bovis and Babesia bigemina. Vector ticks and transmitted parasites are thought to have established unique host-parasite interaction for their survival, meaning that vector ticks may have defensive molecules for the growth control of parasites in their bodies. However, the precise adaptation mechanism of tick-Babesia parasites is still unknown. Recently, cyclophilin A (CyPA) was reported to be important for the development of Babesia parasites in ticks. To reveal a part of their adaptation mechanism, the current study was conducted. An injection of B. bovis-infected RBCs into adult female H. longicornis ticks was found to upregulate the expression profiles of the gene and protein of CyPA in H. longicornis (HlCyPA). In addition, recombinant HlCyPA (rHlCyPA) purified from Escherichia coli exhibited significant inhibitory growth effects on B. bovis and B. bigemina cultivated in vitro, without any hemolytic effect on bovine RBCs at all concentrations used. In conclusion, our results suggest that HlCyPA might play an important role in the growth regulation of Babesia parasites in H. longicornis ticks, during natural acquisition from an infected host. Furthermore, rHlCyPA may be a potential alternative chemotherapeutic agent against babesiosis.

Akt is an essential player in regulating cell/organ growth at the adult stage in the hard tick Haemaphysalis longicornis

Ticks grow rapidly during blood feeding, and their body weight may ultimately increase 100-fold more than that before feeding. The molecular mechanisms controlling growth during blood feeding in ticks remain largely unknown. The conserved insulin/PI3K/Akt signaling pathway regulates growth and metabolism in eukaryotes. Here, we show evidence for the involvement of Akt in growth during blood feeding in the parthenogenetic strain of the hard tick Haemaphysalis longicornis. We identified a homolog of the Ser/Thr kinase Akt (HlAkt) from the EST database of the H. longicornis embryo. HlAkt cDNA had a 1,590 bp ORF that encodes 529 amino acids with a predicted molecular weight of 60 kDa. HlAkt possesses a PH domain, a Ser/Thr kinase domain, a hydrophobic motif, and dual phosphorylation residues (Thr 338 and Ser 503) that are essential for kinase activation. Knockdown of HlAkt by RNA interference caused inhibition of blood feeding in female ticks. Histological observation demonstrated that HlAkt knockdown led to the arrest of growth in internal organs. HlAkt knockdown also affected the expressions of blood meal-induced genes that are essential for blood digestion, development, and reproduction in the female tick. These results strongly indicate that HlAkt is essential to complete the blood feeding process accompanied by the growth of internal organs in adult ticks. This is the first report of identification and characterization of Akt in Chelicerata, including ticks.

Blocking the secretion of saliva by silencing the HlYkt6 gene in the tick Haemaphysalis longicornis

Soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptors (SNAREs) have been identified as the key components of the protein complexes that facilitate vesicle traffic, of which Ykt6 (from Saccharomyces cerevisiae, v-SNARE) is proved to be a multifunctional protein in the membrane fusion. In the present study, a tick homologue of Ykt6 (HlYkt6, predicted 22.6 kDa), was isolated from the ixodid tick Haemaphysalis longicornis. RT-PCR and Western blot analysis indicated that the gene and the encoded protein were expressed ubiquitously in different tissues of the partially fed adult tick. Silencing of the HlYkt6 gene resulted in a significant decrease of the engorged body weight (82.9 +/- 26.8 mg vs. 232.17 +/- 59.1 mg in the PBS-injected control group and 178.7 +/- 57.0 mg in the GFP dsRNA-injected control group) and high mortality of replete ticks (100% in tested group vs. 4.8% in the PBS and 20.4% in GFP dsRNA-injected control groups). Disruption of HlYkt6 mRNA led to the suppression of saliva secretion, and a lower anticoagulant activity of the released liquid from the glands (APTT time: 25.25 +/- 1.50 s) than that of the control groups (39.25 +/- 0.50 s in the PBS-treated group and 40.0 +/- 1.41 s in the GFP dsRNA-treated group). These results suggest the vital role of the HlYkt6 protein in the exocytosis of saliva proteins, the feeding and survival of ticks.