HSC70 from Haemaphysalis flava (Acari: Ixodidae) exerts anticoagulation activity in vitro

Saliva proteome of partially- and fully-engorged adult female Haemaphysalis flava ticks

Tick saliva is a reservoir of bioactive proteins. Saliva protein compositions change dynamically during blood-feeding. Decipherment of protein profiles in different blood-feeding stages may bring deeper insight into tick feeding physiology and provide targets for immunologic control alternatives. However, having the infancy of tick genome sequencing, assembly, annotation, and limited knowledge of tick salivary proteins restrain the data interpretation. Here, we aimed to depict the saliva protein profile in partially- (PE) and fully-engorged (FE) Haemaphysalis flava ticks, with a special focus on the analysis of those uncharacterized proteins. Saliva was collected from PE and FE adult female H. flava ticks. Saliva proteins were analyzed by high-performance liquid chromatography-tandem mass spectrometry (HPLC/MS-MS). MS data were searched against an in-house salivary gland transcriptome library for identification of tick-derived proteins. Abundances of proteins were compared between PE and FE ticks. The uncharacterized proteins detected in saliva were further bioinformatically analyzed. In total, 614 proteins were identified including 94 host proteins and 520 tick-derived proteins. The 226 tick-derived high-confidence proteins were classified into 10 categories: transporters, enzymes, protease inhibitors, immunity-related proteins, lipocalins, glycine-rich proteins, muscle proteins, secreted proteins, uncharacterized proteins and others. A total of 98 proteins were shared in both PE and FE with 74 only in PE and 54 only in FE. Abundances of 24 shared proteins were significantly higher in PE. The profile of top 15 most abundant proteins was also different between PE and FE ticks. The 65 uncharacterized proteins detected in tick saliva were branched into subclusters 1 A, 1B, 2, 3 A, 3B and 3 C based on particular motifs like RGD, LRR, indicating their diverse predicted functions like anti-coagulation, regulation of innate immune, or other functions. This study provides and compares saliva proteomes of H. flava ticks in two feeding stages with special cluster analysis on the uncharacterized proteins. Further investigations are needed to confirm the roles of these uncharacterized proteins in ticks.

Comparative analysis of the anticoagulant activities and immunogenicity of HSC70 and HSC70TKD of Haemaphysalis flava

BACKGROUND

Haemaphysalis flava is a hematophagous ectoparasite that acquires the nutrition needed for development and reproduction by sucking blood and digesting the blood meal. During blood-sucking and blood-meal digestion, the prevention of blood coagulation is important for this tick. Previous studies have shown that heat shock cognate 70 (HSC70) protein has certain anticoagulant activities, but its immunogenicity remains unclear. Also, whether the mutation of individual bases of the TKD-like peptide of HSC70 through the overlap extension method can change its anticoagulant activities and immunogenicity remains to be investigated.

METHODS

The gene encoding the HSC70 protein was cloned from a complementary DNA library synthesized from H. flava. The coding gene of the TKD-like peptide of HSC70 was mutated into a TKD peptide coding gene (HSC70^TKD) using the overlap extension method. Escherichia coli prokaryotic expression plasmids were constructed to obtain the recombinant proteins of HSC70 (rHSC70) and HSC70^TKD (rHSC70^TKD). The purified rHSC70 and rHSC70^TKD were evaluated at different concentrations for anticoagulant activities using four in vitro clotting assays. Emulsifying recombinant proteins with complete and incomplete Freund's adjuvants were subcutaneously immunized in Sprague Dawley rats. The serum antibody titers and serum concentrations of interferon-gamma (IFN-γ) and interleukin-4 (IL-4) were detected using an indirect enzyme-linked immunosorbent assay to assess the immunogenicity of rHSC70 and rHSC70^TKD.

RESULTS

The open reading frame of HSC70 was successfully amplified and found to have a length of 1958 bp. The gene encoding the TKD-like peptide of HSC70 was artificially mutated, with the 1373-position adenine (A) of the original sequence mutated into guanine (G), the 1385-position cytosine (C) mutated into G and the 1386-position G mutated into C. rHSC70 and rHSC70^TKD that fused with His-tag were obtained using the expression plasmids pET-28a-HSC70 and pET-28a-HSC70^TKD, respectively. rHSC70 and rHSC70^TKD prolonged the thrombin time (TT) and reduced the fibrinogen (FIB) content in the plasma, but did not affect the prothrombin time (PT) or activated partial thromboplastin time (APTT) when compared to the negative control. Interestingly, the ability of rHSC70^TKD to prolong the TT and reduce the FIB content in the plasma was better than that of rHSC70. The specific antibody titers of both rHSC70 and rHSC70^TKD in rat serum reached 1:124,000 14 days after the third immunization. The serum concentration of IFN-γ in the rHSC70^TKD group was higher than that in the rHSC70 group. The rHSC70 group has the highest serum concentration of IL-4, and the serum concentration of IL-4 in the rHSC70^TKD group was higher than that in the negative group.

CONCLUSIONS

rHSC70 and rHSC70^TKD exhibited anticoagulant activities by prolonging the TT and reducing the FIB content in vitro. rHSC70^TKD had better anticoagulant activities than rHSC70. Both rHSC70 and rHSC70^TKD had good immunogenicity and induced humoral and cellular immunity.

Protein profiling of hemolymph in Haemaphysalis flava ticks

Background

Tick hemolymph bathes internal organs, acts as an exchange medium for nutrients and cellular metabolites, and offers protection against pathogens. Hemolymph is abundant in proteins. However, there has been limited integrated protein analysis in tick hemolymph thus far. Moreover, there are difficulties in differentiating tick-derived proteins from the host source. The aim of this study was to profile the tick/host protein components in the hemolymph of Haemaphysalis flava.

Methods

Hemolymph from adult engorged H. flava females was collected by leg amputation from the Erinaceus europaeus host. Hemolymph proteins were extracted by a filter-aided sample preparation protocol, digested by trypsin, and assayed by liquid chromatography–tandem mass spectrometry (LC–MS/MS). MS raw data were searched against the UniProt Erinaceidae database and H. flava protein database for host- and tick-derived protein identification. Protein abundance was further quantified by intensity-based absolute quantification (iBAQ).

Results

Proteins extracted from hemolymph unevenly varied in size with intense bands between 100 and 130 kDa. In total, 312 proteins were identified in the present study. Therein 40 proteins were identified to be host-derived proteins, of which 18 were high-confidence proteins. Top 10 abundant host-derived proteins included hemoglobin subunit-α and subunit-β, albumin, serotransferrin-like, ubiquitin-like, haptoglobin, α-1-antitrypsin-like protein, histone H2B, apolipoprotein A-I, and C3-β. In contrast, 169 were high-confidence tick-derived proteins. These proteins were classified into six categories based on reported functions in ticks, i.e., enzymes, enzyme inhibitors, transporters, immune-related proteins, muscle proteins, and heat shock proteins. The abundance of Vg, microplusin and α-2-macroglobulin was the highest among tick-derived proteins as indicated by iBAQ.

Conclusions

Numerous tick- and host-derived proteins were identified in hemolymph. The protein profile of H. flava hemolymph revealed a sophisticated protein system in the physiological processes of anticoagulation, digestion of blood meal, and innate immunity. More investigations are needed to characterize tick-derived proteins in hemolymph.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05287-7.

Tick Saliva and Salivary Glands: What Do We Know So Far on Their Role in Arthropod Blood Feeding and Pathogen Transmission

Ticks are blood-sucking arthropods that have developed myriad of strategies to get a blood meal from the vertebrate host. They first attach to the host skin, select a bite site for a blood meal, create a feeding niche at the bite site, secrete plethora of molecules in its saliva and then starts feeding. On the other side, host defenses will try to counter-attack and stop tick feeding at the bite site. In this constant battle between ticks and the host, arthropods successfully pacify the host and completes a blood meal and then replete after full engorgement. In this review, we discuss some of the known and emerging roles for arthropod components such as cement, salivary proteins, lipocalins, HSP70s, OATPs, and extracellular vesicles/exosomes in facilitating successful blood feeding from ticks. In addition, we discuss how tick-borne pathogens modulate(s) these components to infect the vertebrate host. Understanding the biology of arthropod blood feeding and molecular interactions at the tick-host interface during pathogen transmission is very important. This information would eventually lead us in the identification of candidates for the development of transmission-blocking vaccines to prevent diseases caused by medically important vector-borne pathogens.

Characterization of AV422 from Haemaphysalis flava ticks in vitro

Ticks are hematophagous ectoparasites and cause a major public health threat worldwide. Development of anti-tick vaccines is regarded to be an optimal alternative for tick control. AV422, a unique protein in ticks, is secreted into hosts during blood-feeding, but its roles are not confirmed in Haemaphysalis flava ticks. We retrieved a gene fragment encoding AV422 from a transcriptome dataset of H. flava, and based on it, we reconstructed the full length of AV422 from H. flava (Hf-AV422) by rapid amplification of cDNA ends. Expression profiles of Hf-AV422 in whole ticks and organs of different engorgement levels were determined by qPCR. Then its opening reading frame (ORF) was expressed in Escherichia coli strain BL21 (DE3). The prothrombin time (PT), activated partial thromboplastin time (APTT) and thrombin time (TT) assays were conducted to test anticoagulant activities of the purified recombinant protein (rHf-AV422). The full length of AV422 was 1152 bp. Hf-AV422 showed to be conserved as indicated by multiple sequence alignment. Expression of Hf-AV422 was significantly higher in salivary glands and cuticles than in ovaries. Its expression in whole ticks decreased during engorgement with the highest levels in 1/4 engorged ticks. rHf-AV422 prolonged PT, APTT and TT when incubated with rabbit plasma. Our data demonstrated that Hf-AV422 is a conserved salivary protein with anticoagulant activity. Further studies are needed to test in detail its functional properties to ensure it an adequate antigen candidate for the development of broad-spectrum vaccines against ticks.

Cloning of four HSPA multigene family members in Haemaphysalis flava ticks

The heat shock protein 70 (HSPA) family and their genes have been studied in ticks and are considered as possible antigen candidates for the development of anti-tick vaccines. However, knowledge about their members, structure and function in ticks is incomplete. Based on our transcriptomic data, the full length of four HSPA genes in Haemaphysalis flava (Acari: Ixodidae) was cloned via rapid amplification of cDNA ends. The open reading frame of HSPA2A, HSPA2B, HSPA5 and HSPA9 was 1920, 1911, 1983 and 2088 bp in length, respectively. Three family signatures and one localization motif were in the encoding proteins. HSPA2A and HSPA2B were predicted to be located at cytoplasm/nucleus, whereas HSPA5 and HSPA9 were at endoplasmic reticulum and mitochondria, respectively. In silico simulation demonstrated that those proteins had distinct numbers of α-helixes, extended strands and coils, and different antigenic epitopes. Expression of HSPA5 and HSPA9 in the salivary gland was significantly higher in partially-engorged female adult ticks than the fully-engorged (P < 0.01) as shown by a quantitative polymerase chain reaction. Our data indicated that H. flava ticks had at least four HSPA genes encoding proteins with different cellular locations, structures and expression profiles, suggesting their diverse roles in tick biology.

A survey of proteins in midgut contents of the tick, Haemaphysalis flava, by proteome and transcriptome analysis

Tick blood meals are stored and digested in their midguts. Blood digestion is complex, and many proteins are involved. Study of the tick-derived proteins in the midgut content may aid in the discovery of active molecules that would be useful for anti-tick vaccines. We analyzed the midgut content proteomes of partially engorged female Haemaphysalis flava, fully engorged female H. flava, and hedgehog serum using liquid chromatography tandem-mass spectrometry and label-free quantitation. In this study, high-confidence protein profiling of tick midgut content was determined. Based on the search against our in-house transcriptome database, the 28 high-confidence proteins were identified. Of these, 17 were identified as tick-derived, and the rest were of unspecified origin (proteins that could not be differentiated as host-derived or tick-derived proteins). The function of these midgut content proteins identified here may involve nutrient transportation, anti-coagulation, erythrocyte lysis, detoxification, lipid metabolism, and immunization. The presence of hemoglobin suggested that the red blood cells were lysed in the gut lumen. The midgut contents contain a large amount of fibrinogen and it has the ability to clot immediately. The midgut contained mostly host-derived proteins, and these host proteins provide rich nutrients for tick development and reproduction. However, some intracellular proteins were also identified, suggesting the possibility of shedding of the midgut epithelium and ingestion of saliva during feeding. This finding advances our understanding of the digestive mechanism and will be useful in the screening of vaccine antigens.