Longistatin, an EF-hand Ca2+-binding protein from vector tick: identification, purification, and characterization

Ambivalent Roles of Oxidative Stress in Triangular Relationships among Arthropod Vectors, Pathogens and Hosts

Blood-feeding arthropods, particularly ticks and mosquitoes are considered the most important vectors of arthropod-borne diseases affecting humans and animals. While feeding on blood meals, arthropods are exposed to high levels of reactive oxygen species (ROS) since heme and other blood components can induce oxidative stress. Different ROS have important roles in interactions among the pathogens, vectors, and hosts. ROS influence various metabolic processes of the arthropods and some have detrimental effects. In this review, we investigate the various roles of ROS in these arthropods, including their innate immunity and the homeostasis of their microbiomes, that is, how ROS are utilized to maintain the balance between the natural microbiota and potential pathogens. We elucidate the mechanism of how ROS are utilized to fight off invading pathogens and how the arthropod-borne pathogens use the arthropods’ antioxidant mechanism to defend against these ROS attacks and their possible impact on their vector potentials or their ability to acquire and transmit pathogens. In addition, we describe the possible roles of ROS in chemical insecticide/acaricide activity and/or in the development of resistance. Overall, this underscores the importance of the antioxidant system as a potential target for the control of arthropod and arthropod-borne pathogens.

Characterization of the RAGE-binding protein, Strongyloides venestatin, produced by the silkworm-baculovirus expression system

The receptor for advanced glycation end products (RAGE) recognizes Ca⁺⁺-binding proteins, such as members of the S100 protein family released by dead or devitalized tissues, and plays an important role in inflammatory responses. We recently identified the Ca⁺⁺-binding protein, venestatin, secreted from the rodent parasitic nematode, Strongyloides venezuelensis. We herein characterized recombinant venestatin, which is abundantly produced by the silkworm-baculovirus expression system (silkworm-BES), particularly in its interaction with RAGE. Venestatin from silkworm-BES possessed a binding capacity with Ca⁺⁺ ions and vaccine immunogenicity against S. venezuelensis larvae in mice, which is similar to venestatin produced by the E. coli expression system (EES). Venestatin from silkworm-BES had a higher affinity for human recombinant RAGE than that from EES, and their affinities were Ca⁺⁺-dependent. RAGE in the mouse lung co-immunoprecipitated with venestatin from silkworm-BES administered intranasally, indicating that it bound endogenous mouse RAGE. The present results suggest that venestatin from silkworm-BES affects RAGE-mediated pathological processes.

Venestatin, a Ca++-binding protein from the parasitic nematode Strongyloides venezuelensis, is involved in the larval migration process

The secretory EF-hand Ca⁺⁺-binding proteins act as calcium signaling molecules for control of cell functions, but those proteins from parasitic helminths are poorly understood. Here, we have identified and characterized an EF-hand Ca⁺⁺-binding protein from the rodent nematode, Strongyloides venezuelensis, termed 'venestatin', which is highly conserved in Strongyloides spp. Canonical two EF-hand domains and a signal peptide are present in venestatin. A gel mobility shift assay and Ruthenium red staining indicated that the recombinant venestatin possesses binding ability with Ca⁺⁺ ions. Endogenous venestatin was seemingly localized in the hypodermis and gut of the worms and was found in the excretory-secretory products. Quantitative reverse transcription-PCR data showed that venestatin-specific transcript was upregulated in the parasitic stages of S. venezuelensis, and the upregulation occurred promptly after larval invasion through the host's skin, but not in the case of in vitro incubation. Immunization of mice with recombinant venestatin caused a 55% reduction in larval migration to the lungs, and lung hemorrhaging was mild compared with non-immunized groups, suggesting that anti-venestatin sera may interfere with larval migration from skin to lung. Our results suggest that venestatin is secreted from the hypodermis and gut of S. venezuelensis, and has pivotal roles in larval migration.

Longistatin in tick saliva blocks advanced glycation end-product receptor activation

Ticks are notorious hematophagous ectoparasites and vectors of many deadly pathogens. As an effective vector, ticks must break the strong barrier provided by the skin of their host during feeding, and their saliva contains a complex mixture of bioactive molecules that paralyze host defenses. The receptor for advanced glycation end products (RAGE) mediates immune cell activation at inflammatory sites and is constitutively and highly expressed in skin. Here, we demonstrate that longistatin secreted with saliva of the tick Haemaphysalis longicornis binds RAGE and modulates the host immune response. Similar to other RAGE ligands, longistatin specifically bound the RAGE V domain, and stimulated cultured HUVECs adhered to a longistatin-coated surface; this binding was dramatically inhibited by soluble RAGE or RAGE siRNA. Treatment of HUVECs with longistatin prior to stimulation substantially attenuated cellular oxidative stress and prevented NF-κB translocation, thereby reducing adhesion molecule and cytokine production. Recombinant longistatin inhibited RAGE-mediated migration of mouse peritoneal resident cells (mPRCs) and ameliorated inflammation in mouse footpad edema and pneumonia models. Importantly, tick bite upregulated RAGE ligands in skin, and endogenous longistatin attenuated RAGE-mediated inflammation during tick feeding. Our results suggest that longistatin is a RAGE antagonist that suppresses tick bite-associated inflammation, allowing successful blood-meal acquisition from hosts.

A 24-48 h fed Amblyomma americanum tick saliva immuno-proteome

BACKGROUND

Multiple tick saliva proteins, the majority of which are unknown, confer tick resistance in repeatedly infested animals. The objective of this study was to identify the 24-48 h fed Amblyomma americanum tick saliva immuno-proteome. The 24-48 h tick-feeding phase is critical to tick parasitism as it precedes important events in tick biology, blood meal feeding and disease agent transmission. Fed male, 24 and 96 h fed female phage display cDNA expression libraries were biopanned using rabbit antibodies to 24 and 48 h fed A. americanum female tick saliva proteins. Biopanned immuno-cDNA libraries were subjected to next generation sequencing, de novo assembly, and bioinformatic analysis.

RESULTS

More than 800 transcripts that code for 24-48 h fed A. americanum immuno-proteins are described. Of the 895 immuno-proteins, 52% (464/895) were provisionally identified based on matches in GenBank. Of these, ~19% (86/464) show high level of identity to other tick hypothetical proteins, and the rest include putative proteases (serine, cysteine, leukotriene A-4 hydrolase, carboxypeptidases, and metalloproteases), protease inhibitors (serine and cysteine protease inhibitors, tick carboxypeptidase inhibitor), and transporters and/or ligand binding proteins (histamine binding/lipocalin, fatty acid binding, calreticulin, hemelipoprotein, IgG binding protein, ferritin, insulin-like growth factor binding proteins, and evasin). Others include enzymes (glutathione transferase, cytochrome oxidase, protein disulfide isomerase), ribosomal proteins, and those of miscellaneous functions (histamine release factor, selenoproteins, tetraspanin, defensin, heat shock proteins).

CONCLUSIONS

Data here demonstrate that A. americanum secretes a complex cocktail of immunogenic tick saliva proteins during the first 24-48 h of feeding. Of significance, previously validated immunogenic tick saliva proteins including AV422 protein, calreticulin, histamine release factor, histamine binding/lipocalins, selenoproteins, and paramyosin were identified in this screen, supporting the specificity of the approach in this study. While descriptive, this study opens opportunities for in-depth tick feeding physiology studies.