An insight into the sialome of Simulium guianense (DIPTERA:SIMulIIDAE), the main vector of River Blindness Disease in Brazil

Guianensin, a Simulium guianense salivary protein, has broad anti-hemostatic and anti-inflammatory properties

Background

Salivary glands from blood-feeding arthropods secrete several molecules that inhibit mammalian hemostasis and facilitate blood feeding and pathogen transmission. The salivary functions from Simulium guianense, the main vector of Onchocerciasis in South America, remain largely understudied. Here, we have characterized a salivary protease inhibitor (Guianensin) from the blackfly Simulium guianense.

Materials and methods

A combination of bioinformatic and biophysical analyses, recombinant protein production, in vitro and in vivo experiments were utilized to characterize the molecula mechanism of action of Guianensin. Kinetics of Guianensin interaction with proteases involved in vertebrate inflammation and coagulation were carried out by surface plasmon resonance and isothermal titration calorimetry. Plasma recalcification and coagulometry and tail bleeding assays were performed to understand the role of Guianensin in coagulation.

Results

Guianensin was identified in the sialotranscriptome of adult S. guianense flies and belongs to the Kunitz domain of protease inhibitors. It targets various serine proteases involved in hemostasis and inflammation. Binding to these enzymes is highly specific to the catalytic site and is not detectable for their zymogens, the catalytic site-blocked human coagulation factor Xa (FXa), or thrombin. Accordingly, Guianensin significantly increased both PT (Prothrombin time) and aPTT (Activated partial thromboplastin time) in human plasma and consequently increased blood clotting time ex vivo. Guianensin also inhibited prothrombinase activity on endothelial cells. We show that Guianensin acts as a potent anti-inflammatory molecule on FXa-induced paw edema formation in mice.

Conclusion

The information generated by this work highlights the biological functionality of Guianensin as an antithrombotic and anti-inflammatory protein that may play significant roles in blood feeding and pathogen transmission.

Human immune response against salivary antigens of Simulium damnosum s.l.: A new epidemiological marker for exposure to blackfly bites in onchocerciasis endemic areas

BACKGROUND

Simulium damnosum sensu lato (s.l.) blackflies transmit Onchocerca volvulus, a filarial nematode that causes human onchocerciasis. Human landing catches (HLCs) is currently the sole method used to estimate blackfly biting rates but is labour-intensive and questionable on ethical grounds. A potential alternative is to measure host antibodies to vector saliva deposited during bloodfeeding. In this study, immunoassays to quantify human antibody responses to S. damnosum s.l. saliva were developed, and the salivary proteome of S. damnosum s.l. was investigated.

METHODOLOGY/PRINCIPAL FINDINGS

Blood samples from people living in onchocerciasis-endemic areas in Ghana were collected during the wet season; samples from people living in Accra, a blackfly-free area, were considered negative controls and compared to samples from blackfly-free locations in Sudan. Blackflies were collected by HLCs and dissected to extract their salivary glands. An ELISA measuring anti-S. damnosum s.l. salivary IgG and IgM was optimized and used to quantify the humoral immune response of 958 individuals. Both immunoassays differentiated negative controls from endemic participants. Salivary proteins were separated by gel-electrophoresis, and antigenic proteins visualized by immunoblot. Liquid chromatography mass spectrometry (LC-MS/MS) was performed to characterize the proteome of S. damnosum s.l. salivary glands. Several antigenic proteins were recognized, with the major ones located around 15 and 40 kDa. LC-MS/MS identified the presence of antigen 5-related protein, apyrase/nucleotidase, and hyaluronidase.

CONCLUSIONS/SIGNIFICANCE

This study validated for the first time human immunoassays that quantify humoral immune responses as potential markers of exposure to blackfly bites. These assays have the potential to facilitate understanding patterns of exposure as well as evaluating the impact of vector control on biting rates. Future studies need to investigate seasonal fluctuations of these antibody responses, potential cross-reactions with other bloodsucking arthropods, and thoroughly identify the most immunogenic proteins.

Characterization of IgE-binding proteins in the salivary glands of Simulium nigrogilvum (Diptera: Simuliidae)

Simulium dermatitis is an IgE-mediated skin reaction in animals and humans caused by the bites of black flies. Although Simulium nigrogilvum has been incriminated as the main human-biting black fly species in Thailand, information on its salivary allergens is lacking. Salivary gland extract of S. nigrogilvum females was subjected to sodium dodecylsulfate-polyacrylamide gel electrophoresis, and the separated components were applied onto nitrocellulose membranes for immunoblotting, which was performed by probing the protein blots with sera from 17 individuals who were allergic to the bites of S. nigrogilvum. IgE-reactive protein bands were characterized further by liquid chromatography-mass spectrometry (LC-MS/MS) analysis. Nine protein bands (79, 42, 32, 25, 24, 22, 15, 13, and 11 kDa) were recognized in the serum of the subjects. Four of the nine protein bands (32, 24, 15, and 11 kDa) showed IgE reactivity in all (100%) of the tested sera, and they were identified as salivary secreted antigen 5-related protein, salivary serine protease, erythema protein, and hypothetical secreted protein, respectively. Three other proteins, salivary serine protease (25 kDa), salivary D7 secreted protein (22 kDa), and hypothetical protein (13 kDa), reacted with > 50% of the sera. The relevance of the identified protein bands as allergens needs to be confirmed by using pure recombinant proteins, either in the in vivo skin prick test or in vitro detection of the specific IgE in the serum samples of allergic subjects. This will be useful for the rational design of component-resolved diagnosis and allergen immunotherapy for the allergy mediated by the bites of black flies.

Proteomes of the female salivary glands of Simulium nigrogilvum and Simulium nodosum, the main human-biting black flies in Thailand

Although several studies have reported pharmacological and immunological activity, as well as the role of black flies in transmitting pathogens to vertebrate hosts through salivary glands (SG) during blood feeding, SG proteomes of the anthropophilic black flies in Thailand have never been reported. Therefore, this study determined the SG proteomes of female S. nigrogilvum and S. nodosum. Sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) and two-dimensional (2-DE) gels containing separated SG proteins of individual species were subjected to liquid chromatography-tandem mass spectrometry (LCMS/MS) and an orthologous protein search from eukaryotic organism, nematocera and simuliidae databases for total protein identification. SDS-PAGE and protein staining revealed at least 13 and 9 major protein bands in the SGs of female S. nigrogilvum and S. nodosum, respectively, as well as several minor ones. The 2-DE demonstrated a total of 56 and 41 protein spots for S. nigrogilvum and S. nodosum, respectively. Most of the proteins obtained in both species were enzymes involved in blood feeding, including proteases, apyrases, hyaluronidases, aminopeptidase and elastase. The results obtained in this study provided a new body of knowledge for a better understanding on the role of salivary gland proteins in these black fly species in Thailand.

The salivary hyaluronidase and apyrase of the sand fly Sergentomyia schwetzi (Diptera, Psychodidae)

Current knowledge of sand fly salivary components has been based solely on Lutzomyia and Phlebotomus species which feed mainly on mammals; their hyaluronidases and apyrases were demonstrated to significantly affect blood meal intake and transmission of vector-borne pathogens. Members of the third sand fly genus Sergentomyia preferentially feed on reptiles but some of them are considered as Leishmania and arboviruses vectors; however, nothing is known about their salivary components that might be relevant for pathogens transmission. Here, marked hyaluronidase and apyrase activities were demonstrated in the saliva of a Sergentomyia schwetzi colony maintained on geckos. Hyaluronidase of S. schwetzi cleaved hyaluronan as the prominent substrate, and was active over a broad pH range from 4.0 to 8.0, with a sharp peak at pH 5.0. SDS PAGE zymography demonstrated the monomeric character of the enzyme, which remained active in reducing conditions. The apparent molecular weight of 43 kDa was substantially lower than in any sand fly species tested so far and may indicate relatively low grade of the glycosylation of the enzyme. The apyrase of S. schwetzi was typical strictly Ca2+ dependent Cimex-family apyrase. It was active over a pH range from 6.5 to 9.0, with a peak of activity at pH 8.5, and had an ATPase/ADPase ratio of 0.9. The apyrase activity increased during the first 3 days post-emergence, then reached a plateau and remained relatively constant until day 8. In comparison with a majority of Phlebotomus and Lutzomyia species tested to date, both the hyaluronidase and apyrase activities of S. schwetzi were relatively low, which may reflect an adaptation of this sand fly to blood feeding on non-mammalian hosts.

Chromosomal Translocations in Black Flies (Diptera: Simuliidae)-Facilitators of Adaptive Radiation?

A macrogenomic investigation of a Holarctic clade of black flies-the Simulium cholodkovskii lineage-provided a platform to explore the implications of a unique, synapomorphic whole-arm interchange in the evolution of black flies. Nearly 60 structural rearrangements were discovered in the polytene complement of the lineage, including 15 common to all 138 analyzed individuals, relative to the central sequence for the entire subgenus Simulium. Three species were represented, of which two Palearctic entities (Simulium cholodkovskii and S. decimatum) were sympatric; an absence of hybrids confirmed their reproductive isolation. A third (Nearctic) entity had nonhomologous sex chromosomes, relative to the other species, and is considered a separate species, for which the name Simulium nigricoxum is revalidated. A cytophylogeny is inferred and indicates that the two Palearctic taxa are sister species and these, in turn, are the sister group of the Nearctic species. The rise of the S. cholodkovskii lineage encompassed complex chromosomal and genomic restructuring phenomena associated with speciation in black flies, viz. expression of one and the same rearrangement as polymorphic, fixed, or sex linked in different species; taxon-specific differentiation of sex chromosomes; and reciprocal translocation of chromosome arms. The translocation is hypothesized to have occurred early in male spermatogonia, with the translocated chromosomal complement being transmitted to the X- and Y-bearing sperm during spermatogenesis, resulting in alternate disjunction of viable F1 translocation heterozygotes and the eventual formation of more viable and selectable F2 translocation homozygous progeny. Of 11 or 12 independently derived whole-arm interchanges known in the family Simuliidae, at least six are associated with subsequent speciation events, suggesting a facilitating role of translocations in adaptive radiations. The findings are discussed in the context of potential structural and functional interactions for future genomic research.

A cecropin-like antimicrobial peptide with anti-inflammatory activity from the black fly salivary glands

BACKGROUND

Several antimicrobial peptides (AMPs) belonging to the cecropin family have been identified from the salivary glands of different black fly species, however, the immunological functions for these molecules were poorly understood.

METHODS

A novel cecropin-like antimicrobial peptide (SibaCec) was purified using reverse phase high-performance liquid chromatography (RP-HPLC) from the salivary glands of the black fly Simulium bannaense. The amino acid sequence of SibaCec was determined by a combination method of automated Edman degradation and cDNA sequencing. The morphologic changes of Gram-negative bacteria Escherichia coli treated with SibaCec were assessed by scanning electron microscopy (SEM). Quantitative PCR (qPCR) was performed to analyze the mRNA expression of the inducible NO synthase (iNOS) and pro-inflammatory cytokines. Nitric oxide (NO) generation was examined using a Griess assay and the secretion of pro-inflammatory cytokines was determined by an enzyme-linked immunosorbent assay (ELISA). The activation of extracellular signal-regulated kinase (ERK), p38, and the nuclear translocation of nuclear factor-kappaB (NF-κB) were assessed by Western blotting analysis. Circular dichroism (CD) spectroscopy was performed to evaluate the secondary structure of SibaCec in solvent environment. Interaction of SibaCec with lipopolysaccharide (LPS) was studied using fluorescein isothiocyanate (FITC)- conjugated LPS aggregates. Neutralization of LPS by SibaCec was assayed with the chromogenic limulus amebocyte lysate (LAL) test. qPCR was also used to analyze the expression of SibaCec mRNA in the salivary glands of insects after oral infection with the bacteria E.coli.

RESULTS

SibaCec possessed potent antimicrobial activity against Gram-negative bacteria, and showed low cytotoxicity toward mammalian cells. SEM analysis indicated that SibaCec killed bacteria through the disruption of cell membrane integrity. Furthermore, SibaCec significantly inhibited lipopolysaccharide (LPS)-induced production of NO and pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α), interferon-1β (IL-1β) and interferon-6 (IL-6) by blocking the activation of MAPKs and NF-κB signaling pathways. It mainly adopted an α-helix conformation in membrane-mimetic environments. SibaCec could interact and neutralize LPS. Infection of black flies with bacteria caused an upregulation of the expression of SibaCec.

CONCLUSIONS

These results demonstrated that in addition to the bactericidal capacity, SibaCec can function as immune regulator, inhibiting host secretion of inflammatory factors.

Arthropod venom Hyaluronidases: biochemical properties and potential applications in medicine and biotechnology

Hyaluronidases are enzymes that mainly degrade hyaluronan, the major glycosaminoglycan of the interstitial matrix. They are involved in several pathological and physiological activities including fertilization, wound healing, embryogenesis, angiogenesis, diffusion of toxins and drugs, metastasis, pneumonia, sepsis, bacteremia, meningitis, inflammation and allergy, among others. Hyaluronidases are widely distributed in nature and the enzymes from mammalian spermatozoa, lysosomes and animal venoms belong to the subclass EC 3.2.1.35. To date, only five three-dimensional structures for arthropod venom hyaluronidases (Apis mellifera and Vespula vulgaris) were determined. Additionally, there are four molecular models for hyaluronidases from Mesobuthus martensii, Polybia paulista and Tityus serrulatus venoms. These enzymes are employed as adjuvants to increase the absorption and dispersion of other drugs and have been used in various off-label clinical conditions to reduce tissue edema. Moreover, a PEGylated form of a recombinant human hyaluronidase is currently under clinical trials for the treatment of metastatic pancreatic cancer. This review focuses on the arthropod venom hyaluronidases and provides an overview of their biochemical properties, role in the envenoming, structure/activity relationship, and potential medical and biotechnological applications.

A mosquito lipoxin/lipocalin complex mediates innate immune priming in Anopheles gambiae

Exposure of Anopheles gambiae mosquitoes to Plasmodium infection enhances the ability of their immune system to respond to subsequent infections. However, the molecular mechanism that allows the insect innate immune system to ‘remember' a previous encounter with a pathogen has not been established. Challenged mosquitoes constitutively release a soluble haemocyte differentiation factor into their haemolymph that, when transferred into Naive mosquitoes, also induces priming. Here we show that this factor consists of a Lipoxin/Lipocalin complex. We demonstrate that innate immune priming in mosquitoes involves a persistent increase in expression of Evokin (a lipid carrier of the lipocalin family), and in their ability to convert arachidonic acid to lipoxins, predominantly Lipoxin A₄. Plasmodium ookinete midgut invasion triggers immune priming by inducing the release of a mosquito lipoxin/lipocalin complex.

A soluble factor induced by Plasmodium infection promotes hemocyte differentiation and increases mosquitoe resistance to subsequent infections. Here the authors show that this factor consists of a Lipocalin/Lipoxin A4 complex, and that insects can metabolize arachidonic acid to produce lipoxins.

Purification and characterization of a novel defensin from the salivary glands of the black fly, Simulium bannaense

Background

Black flies (Diptera: Simuliidae) are haematophagous insects that can cause allergic reactions and act as vectors of pathogens. Although their saliva has been thought to contain a diverse array of physiologically active molecules, little information is available on antimicrobial factors in black fly salivary glands, especially no defensins have been reported so far.

Methods

A novel cationic defensin designated SibaDef was purified using reverse phase high-performance liquid chromatography (RP-HPLC) from the salivary glands of the black fly Simulium bannaense. The amino acid sequence of SibaDef was determined by a combination method of automated Edman degradation and cDNA sequencing. The morphologic changes of Gram-positive bacteria Staphylococcus aureus or Bacillus subtilis treated with SibaDef were assessed by scanning electron microscopy (SEM). Quantitative PCR (qPCR) was performed to analyze the expression of SibaDef mRNA in whole bodies of insects after oral infection with the bacteria S. aureus or B. subtilis.

Results

Surprisingly, the phylogenetic analysis of defensin-related amino acid sequences demonstrated that SibaDef is most closely related to defensins from the human body louse Pediculus humanus corporis (Anoplura: Pediculidae), rather than to other dipteran defensins. SibaDef showed potent antimicrobial activities against Gram-positive bacteria with minimal inhibitory concentrations (MICs) ranging from 0.83 μM to 2.29 μM. SEM analysis indicated that SibaDef killed microorganisms through the disruption of cell membrane integrity. The transcript levels of SibaDef in the bacteria-immunized flies increased with the time course, reaching maximum at 36 h and then slowly decreased from that time point.

Conclusions

Our results indicate that SibaDef is involved in the innate humoral response of the black fly S. bannaense, and it might play a significant role in the defence against microorganisms in both sugar and blood meals.

Heterochromatin and sibling species of Simulium praelargum s.l. (Diptera: Simuliidae)

Cytological descriptions are given for two sympatric sibling species, Simulium praelargum IIIL-st and Simulium praelargum IIIL-1.2, from Darjeeling, West Bengal, India. Sibling IIIL-1.2 differs from IIIL-st by a two step fixed included inversion (IIIL-1.2) found on the long arm of chromosome III. Both siblings possess heterochromatinized IIIS polytene chromosome ends, while IIIL-1.2 is unique within the Simuliidae in that it exhibits a very large enhanced chromocentre that persists in normal somatic tissue, contrary to other chromocentre-containing taxa. In IIIL-1.2, the chromocentre occurs as a positively allocyclic heteropycnotic body in normal mitotic interphase cells of neuroblast ganglia, oogonia, and spermatogonia. In mitotic metaphase chromosomes, the chromocentre forms large pronounced primary (centromere) constrictions and appears to be associated with nonhomologous pairing. Initial cytological studies on taxa within the feuerborni group have revealed heterochromatic chromosomal polymorphisms. Progressive fixation of these polymorphisms in different taxa within the group opens up the possibility of using comparative molecular or genomic approaches to begin to define the functional and structural aspects of the epigenome and to further characterize mitosis and meiosis in S. praelargum IIIL-1.2.

Simplagrin, a platelet aggregation inhibitor from Simulium nigrimanum salivary glands specifically binds to the Von Willebrand factor receptor in collagen and inhibits carotid thrombus formation in vivo

BACKGROUND

Among the several challenges faced by bloodsucking arthropods, the vertebrate hemostatic response against blood loss represents an important barrier to efficient blood feeding. Here we report the first inhibitor of collagen-induced platelet aggregation derived from the salivary glands of a black fly (Simulium nigrimanum), named Simplagrin.

METHODS AND FINDINGS

Simplagrin was expressed in mammalian cells and purified by affinity-and size-exclusion chromatography. Light-scattering studies showed that Simplagrin has an elongated monomeric form with a hydrodynamic radius of 5.6 nm. Simplagrin binds to collagen (type I-VI) with high affinity (2-15 nM), and this interaction does not involve any significant conformational change as determined by circular dichroism spectroscopy. Simplagrin-collagen interaction is both entropically and enthalpically driven with a large negative ΔG, indicating that this interaction is favorable and occurs spontaneously. Simplagrin specifically inhibits von Willebrand factor interaction with collagen type III and completely blocks platelet adhesion to collagen under flow conditions at high shear rates; however, Simplagrin failed to block glycoprotein VI and Iα2β1 interaction to collagen. Simplagrin binds to RGQOGVMGF peptide with an affinity (K(D) 11 nM) similar to that of Simplagrin for collagen. Furthermore, Simplagrin prevents laser-induced carotid thrombus formation in vivo without significant bleeding in mice and could be useful as an antithrombotic agent in thrombosis related disease.

CONCLUSION

Our results support the orthology of the Aegyptin clade in bloodsucking Nematocera and the hypothesis of a faster evolutionary rate of salivary function of proteins from blood feeding arthropods.

Collagen-binding protein, Aegyptin, regulates probing time and blood feeding success in the dengue vector mosquito, Aedes aegypti

Mosquito salivary glands have important roles in blood feeding and pathogen transmission. However, the biological relevance of many salivary components has yet to be determined. Aegyptin, a secreted salivary protein from Aedes aegypti, binds collagen and inhibits platelet aggregation and adhesion. We used a transgenic approach to study the relevance of Aegyptin in mosquito blood feeding. Aedes aegypti manipulated genetically to express gene-specific inverted-repeat RNA sequences exhibited significant reductions in Aegyptin mRNA accumulation (85-87%) and protein levels (>80-fold) in female mosquito salivary glands. Transgenic mosquitoes had longer probing times (78-300 s, P < 0.0001) when feeding on mice compared with controls (15-56 s), feeding success was reduced, and those feeding took smaller blood meals. However, no differences in feeding success or blood meal size were found in membrane feeding experiments using defibrinated human blood. Salivary gland extracts from transgenic mosquitoes failed to inhibit collagen-induced platelet aggregation in vitro. Reductions of Aegyptin did not affect salivary ADP-induced platelet aggregation inhibition or disturb anticlotting activities. Our results demonstrate the relevance of Aegyptin for A. aegypti blood feeding, providing further support for the hypothesis that platelet aggregation inhibition is a vital salivary function in blood feeding arthropods. It has been suggested that the multiple mosquito salivary components mediating platelet aggregation (i.e., Aegyptin, apyrase, D7) represent functional redundancy. Our findings do not support this hypothesis; instead, they indicate that multiple salivary components work synergistically and are necessary to achieve maximum blood feeding efficiency.

A deep insight into the sialotranscriptome of the mosquito, Psorophora albipes

Background

Psorophora mosquitoes are exclusively found in the Americas and have been associated with transmission of encephalitis and West Nile fever viruses, among other arboviruses. Mosquito salivary glands represent the final route of differentiation and transmission of many parasites. They also secrete molecules with powerful pharmacologic actions that modulate host hemostasis, inflammation, and immune response. Here, we employed next generation sequencing and proteome approaches to investigate for the first time the salivary composition of a mosquito member of the Psorophora genus. We additionally discuss the evolutionary position of this mosquito genus into the Culicidae family by comparing the identity of its secreted salivary compounds to other mosquito salivary proteins identified so far.

Results

Illumina sequencing resulted in 13,535,229 sequence reads, which were assembled into 3,247 contigs. All families were classified according to their in silico-predicted function/ activity. Annotation of these sequences allowed classification of their products into 83 salivary protein families, twenty (24.39%) of which were confirmed by our subsequent proteome analysis. Two protein families were deorphanized from Aedes and one from Ochlerotatus, while four protein families were described as novel to Psorophora genus because they had no match with any other known mosquito salivary sequence. Several protein families described as exclusive to Culicines were present in Psorophora mosquitoes, while we did not identify any member of the protein families already known as unique to Anophelines. Also, the Psorophora salivary proteins had better identity to homologs in Aedes (69.23%), followed by Ochlerotatus (8.15%), Culex (6.52%), and Anopheles (4.66%), respectively.

Conclusions

This is the first sialome (from the Greek sialo = saliva) catalog of salivary proteins from a Psorophora mosquito, which may be useful for better understanding the lifecycle of this mosquito and the role of its salivary secretion in arboviral transmission.

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