Surface associated antigens of Dirofilaria immitis adult worms activate the host fibrinolytic system

A Comparative Analysis of the Protein Cargo of Extracellular Vesicles from Helminth Parasites

Helminth parasites cause debilitating-sometimes fatal-diseases in humans and animals. Despite their impact on global health, mechanisms underlying host-parasite interactions are still poorly understood. One such mechanism involves the exchange of extracellular vesicles (EVs), which are membrane-enclosed subcellular nanoparticles. To date, EV secretion has been studied in helminth parasites, including EV protein content. However, information is highly heterogeneous, since it was generated in multiple species, using varied protocols for EV isolation and data analysis. Here, we compared the protein cargo of helminth EVs to identify common markers for each taxon. For this, we integrated published proteomic data and performed a comparative analysis through an orthology approach. Overall, only three proteins were common in the EVs of the seven analyzed species. Additionally, varied repertoires of proteins with moonlighting activity, vaccine antigens, canonical and non-canonical proteins related to EV biogenesis, taxon-specific proteins of unknown function and RNA-binding proteins were observed in platyhelminth and nematode EVs. Despite the lack of consensus on EV isolation protocols and protein annotation, several proteins were shown to be consistently detected in EV preparations from organisms at different taxa levels, providing a starting point for a selective biochemical characterization.

Involvement of the excretory/secretory and surface-associated antigens of Dirofilaria immitis adult worms in the angiogenic response in an in-vitro endothelial cell model

Angiogenesis is a process by which new vessels are formed from pre-existing ones when the physiological conditions of the vascular endothelium are altered. Heartworm disease, caused by Dirofilaria immitis, causes changes in the vascular endothelium of the pulmonary arteries due to obstruction, friction, and hypoxia. The aim of this study was to analyze whether the excretory/secretory and surface-associated antigens of adult worms interact and modulates the angiogenic mechanism, viable cell number and cell migration, as well as the formation of pseudo-capillaries. Cultures of human vascular endothelial cells (HUVECs) stimulated with excretory/secretory antigens (DiES), surface-associated antigens (Cut) from D. immitis adult worms, VEFG-A (Vascular Endothelial Growth Factor A), as well as DiES+VEFG-A and Cut+VEFG-A were used. The production of VEFG-A and other proangiogenic [soluble VEFGR-2 (sVEFGR-2), membrane Endoglin (mEndoglin)] and antiangiogenic [VEFGR-1/soluble Flt (sFlt), soluble Endoglin (sEndoglin)] molecules was assessed using commercial ELISA kits. Cell viability was analyzed by live cell count and cytotoxicity assays by a commercial kit. In addition, viable cell number by MTT-based assay, cell migration by wound-healing assay carrying out scratched wounds, and the capacity of pseudo-capillary formation to analyze cell connections and cell groups in Matrigel cell cultures, were evaluated. In all cases, non‑stimulated cultures were used as controls. DiES+VEFG-A and Cut+VEFG-A significantly increased the production of VEFG-A and sVEFGR-2, and only Cut+VEFG-A significantly increased the production of VEFGR-1/sFlt compared to other groups and non-stimulated cultures. Moreover, only DiES+VEFG-A produced a significant increase in viable cell number and significant decrease cell migration, as well as in the organization and number of cell connections. Excretory/secretory and surface-associated antigens of adult D. immitis activated the angiogenic mechanism by mainly stimulating the synthesis of proangiogenic factors, and only excretory/secretory antigens increased viable cell number, activated cell migration and the formation of pseudo-capillaries. These processes could lead to vascular endothelial remodeling of the infected host and favor the long-term survival of the parasite.

Hemostatic Dysfunction in Dogs Naturally Infected with Angiostrongylus vasorum—A Narrative Review

This narrative review aims to describe Angiostrongylus vasorum-induced hemostatic dysfunction of dogs with emphasis on clinical and laboratory findings as well as potential therapeutic strategies for the bleeding patient. Canine angiostrongylosis (CA) is a disease with potentially high morbidity and mortality in endemic areas and with fatal outcome often associated with either severe respiratory compromise, pulmonary hypertension and right-sided heart failure, or hemostatic dysfunction with severe bleeding. The most common signs of hemorrhage are hematomas, petecchiation, ecchymoses, oral mucosal membrane bleeding and scleral bleeding, while intracranial and pulmonary hemorrhage are among the most severe. The pathophysiological mechanisms underlying hemostatic dysfunction in these patients are presently researched. While the larval effect on platelets remains unknown, the parasite appears to induce dysregulation of hemostatic proteins, with studies suggesting a mixture of pro-coagulant protein consumption and hyperfibrinolysis. Importantly, not all dogs display the same hemostatic abnormalities. Consequently, characterizing the hemostatic state of the individual patient is necessary, but has proven difficult with traditional coagulation tests. Global viscoelastic testing shows promise, but has limited availability in general practice. Treatment of A. vasorum-infected dogs with hemostatic dysfunction relies on anthelmintic treatment as well as therapy directed at the individual dog’s specific hemostatic alterations.

The Immunological Role of Vascular and Lymphatic Endothelial Cells in Filarial Infections

Simple Summary

The endothelium is a monolayer of cells forming a thin membrane that lines the inside of blood vessels. These cells release molecules that regulate vascular relaxation, contraction, and can control blood clotting and the immune response. During infections with filarial nematodes, common parasites of humans and animals, the endothelium is believed to play a key role in the communication between the host and the parasite, since the embryonic stage of filaroids is distributed in the bloodstream. Therefore, this review aims to gather research from different scientists in order to better understand the host immune response in infections with filarial nematodes.

Abstract

The embryonic stage of filarial nematodes, or microfilariae (Mf), shows daily and seasonal periodicity that requires their migration through blood vessels into the lungs, where they are sequestered when not circulating in the peripheral blood. Therefore, Mf and the host endothelium are likely in a permanent state of hide and seek. Interestingly, filarial nematodes co-cultured in media with a murine endothelial cell line survive eight times longer than those cultured in media alone. This suggests that the endothelium is an important element of the immune response in filarial nematodes, perversely promoting their survival in the host. In this review, we will focus on potential pathways involved in the relationship between filarial nematodes and the host endothelium, including the role of endothelial ICAM/VCAM/PECAM adhesion molecules, surface markers involved in the passage of Mf through host tissue, anti-thrombolic effects caused by the presence of filarial nematodes (including plasmins), endothelial cell proliferation (VEGF), and other aspects of the immune activation of the endothelium. The aim of this review is to merge the knowledge about the cross-talk between Mf of different filarial nematode species and endothelial cells (EC), thus allowing a better understanding of the mechanism of these parasitic infections.

The Angiostrongylus vasorum Excretory/Secretory and Surface Proteome Contains Putative Modulators of the Host Coagulation

Angiostrongylus vasorum is a cardiopulmonary nematode of canids and is, among others, associated with bleeding disorders in dogs. The pathogenesis of such coagulopathies remains unclear. A deep proteomic characterization of sex specific A. vasorum excretory/secretory proteins (ESP) and of cuticular surface proteins was performed, and the effect of ESP on host coagulation and fibrinolysis was evaluated in vitro. Proteins were quantified by liquid chromatography coupled to mass spectrometry and functionally characterized through gene ontology and pathway enrichment analysis. In total, 1069 ESP (944 from female and 959 from male specimens) and 1195 surface proteins (705 and 1135, respectively) were identified. Among these were putative modulators of host coagulation, e.g., von Willebrand factor type D domain protein orthologues as well as several proteases, including serine type proteases, protease inhibitors and proteasome subunits. The effect of ESP on dog coagulation and fibrinolysis was evaluated on canine endothelial cells and by rotational thromboelastometry (ROTEM). After stimulation with ESP, tissue factor and serpin E1 transcript expression increased. ROTEM revealed minimal interaction of ESP with dog blood and ESP did not influence the onset of fibrinolysis, leading to the conclusion that Angiostrongylus vasorum ESP and surface proteins are not solely responsible for bleeding in dogs and that the interaction with the host's vascular hemostasis is limited. It is likely that coagulopathies in A. vasorum infected dogs are the result of a multifactorial response of the host to this parasitic infection.

Multifunctional Fructose 1,6-Bisphosphate Aldolase as a Therapeutic Target

Fructose 1,6-bisphosphate aldolase is a ubiquitous cytosolic enzyme that catalyzes the fourth step of glycolysis. Aldolases are classified into three groups: Class-I, Class-IA, and Class-II; all classes share similar structural features but low amino acid identity. Apart from their conserved role in carbohydrate metabolism, aldolases have been reported to perform numerous non-enzymatic functions. Here we review the myriad "moonlighting" functions of this classical enzyme, many of which are centered on its ability to bind to an array of partner proteins that impact cellular scaffolding, signaling, transcription, and motility. In addition to the cytosolic location, aldolase has been found the extracellular surface of several pathogenic bacteria, fungi, protozoans, and metazoans. In the extracellular space, the enzyme has been reported to perform virulence-enhancing moonlighting functions e.g., plasminogen binding, host cell adhesion, and immunomodulation. Aldolase's importance has made it both a drug target and vaccine candidate. In this review, we note the several inhibitors that have been synthesized with high specificity for the aldolases of pathogens and cancer cells and have been shown to inhibit classical enzyme activity and moonlighting functions. We also review the many trials in which recombinant aldolases have been used as vaccine targets against a wide variety of pathogenic organisms including bacteria, fungi, and metazoan parasites. Most of such trials generated significant protection from challenge infection, correlated with antigen-specific cellular and humoral immune responses. We argue that refinement of aldolase antigen preparations and expansion of immunization trials should be encouraged to promote the advancement of promising, protective aldolase vaccines.

Blood loss and coagulation profile in pregnant and non-pregnant queens undergoing elective ovariohysterectomy

OBJECTIVES

The aims of this study were to determine if there is increased risk of intraoperative bleeding in pregnant cats undergoing elective ovariohysterectomy (OHE), and to compare coagulation in queens in various stages of estrus and pregnancy subjected to elective OHE using a whole-blood viscoelastic assay.

METHODS

Intraoperative blood loss was compared between non-pregnant and pregnant cats undergoing elective OHE. Viscoelastic evaluations of whole blood drawn pre- and postoperatively were performed using a point-of-care device measuring clot time (CT), clot formation time (CFT), alpha angle, maximum clot formation (MCF), amplitude at 10 and 20 mins (A10 and A20, respectively), and lysis index at 30 and 45 mins after MCF (LI30 and LI45, respectively).

RESULTS

One hundred and ninety-three cats underwent OHE by a ventral midline approach. Median blood loss was greater for pregnant cats (2.0 ml, range <0.5-13 ml) than non-pregnant cats (<0.5 ml, range <0.5-15 ml; P <0.0001). Preoperatively, pregnant cats had a shorter median CFT (165 s vs 190.5 s), increased median A10 (31 from 25.5 VCM units) and A20 (38 from 35 VCM units), and a lower median LI45 (99% from 100%) than non-pregnant cats. Postoperatively, A10 and A20 increased, and LI30 and LI45 decreased in both non-pregnant and pregnant queens. In pregnant queens, mean CT also increased postoperatively.

CONCLUSIONS AND RELEVANCE

Pregnant cats were relatively hypercoagulable and had an increased rate of clot lysis than non-pregnant cats. Intraoperative blood loss was increased in pregnant vs non-pregnant cats, but no clinically relevant bleeding conditions occurred.

Angiogenesis in cardiopulmonary dirofilariosis: does the Wolbachia surface protein have a pro- or anti-angiogenic effect?

Cardiopulmonary dirofilariosis caused by Dirofilaria immitis produces inflammation, blood vessel obstruction and hypoxia, which are required conditions for the beginning of the process of neovascularization. Since D. immitis harbours intracellular symbiotic Wolbachia bacterium, the global understanding of the angiogenic process requires the analysis of the effect of the parasite molecules, but also that of Wolbachia. Canine primary lung microvascular endothelial cells were treated with the recombinant Wolbachia surface protein (rWSP) and the expression of angiogenic factors like Vascular Endothelial Growth Factor-A (VEGF-A), sFlt, membrane Endoglin (mEndoglin) and soluble Endoglin (sEndoglin), as well as the in vitro formation of pseudocapillaries, were measured. The analyses showed a significant increase in the expression of pro-angiogenic VEGF-A and anti-angiogenic sEndoglin, together with a significant decrease in both pro-angiogenic mEndoglin and pseudocapillary formation, compared to untreated controls. Due to the complexity of the angiogenic process and its relationship with other physiological processes like inflammation and fibrinolysis, these results might suggest that rWSP participate in various mechanisms related to each other and its effects might depend either on the balance between them or on the moment of their occurrence.

Pro-fibrinolytic potential of the third larval stage of Ascaris suum as a possible mechanism facilitating its migration through the host tissues

Background

Ascaris roundworms are the parasitic nematodes responsible for causing human and porcine ascariasis. Whereas A. lumbricoides is the most common soil-transmitted helminth infecting humans in the world, A. suum causes important economic losses in the porcine industry. The latter has been proposed as a model for the study of A. lumbricoides since both species are closely related. The third larval stage of these parasites carries out an intriguing and complex hepatopulmonary route through the bloodstream of its hosts. This allows the interaction between larvae and the physiological mechanisms of the hosts circulatory system, such as the fibrinolytic system. Parasite migration has been widely linked to the activation of this system by pathogens that are able to bind plasminogen and enhance plasmin generation. Therefore, the aim of this study was to examine the interaction between the infective third larval stage of A. suum and the host fibrinolytic system as a model of the host-Ascaris spp. relationships.

Methods

Infective larvae were obtained after incubating and hatching fertile eggs of A. suum in order to extract their cuticle and excretory/secretory antigens. The ability of both extracts to bind and activate plasminogen, as well as promote plasmin generation were assayed by ELISA and western blot. The location of plasminogen binding on the larval surface was revealed by immunofluorescence. The plasminogen-binding proteins from both antigenic extracts were revealed by two-dimensional electrophoresis and plasminogen-ligand blotting, and identified by mass spectrometry.

Results

Cuticle and excretory/secretory antigens from infective larvae of A. suum were able to bind plasminogen and promote plasmin generation in the presence of plasminogen activators. Plasminogen binding was located on the larval surface. Twelve plasminogen-binding proteins were identified in both antigenic extracts.

Conclusions

To the best of our knowledge, the present results showed for the first time, the pro-fibrinolytic potential of infective larvae of Ascaris spp., which suggests a novel parasite survival mechanism by facilitating the migration through host tissues.

Schistosoma mansoni glyceraldehyde-3-phosphate dehydrogenase enhances formation of the blood-clot lysis protein plasmin

Schistosomes are intravascular blood flukes that cause the parasitic disease schistosomiasis. In agreement with Schistosoma mansoni (Sm) proteomic analysis, we show here that the normally intracellular glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is also found at the parasite surface; live worms from all intravascular life stages display GAPDH activity. Suppressing GAPDH gene expression using RNA interference significantly lowers this live worm surface activity. Medium in which the worms are cultured overnight displays essentially no activity, showing that the enzyme is not shed or excreted but remains associated with the worm surface. Immunolocalization experiments confirm that the enzyme is highly expressed in the parasite tegument (skin). Surface activity in schistosomula amounts to ∼8% of that displayed by equivalent parasite lysates. To address the functional role of SmGAPDH, we purified the protein following its expression in Escherichiacoli strain DS113. The recombinant protein displays optimal enzymatic activity at pH 9.2, shows robust activity at the temperature of the parasite's hosts, and has a Michaelis-Menten constant for glyceraldehyde-3-phosphate (GAP) of 1.4 mM±0.24. We show that recombinant SmGAPDH binds plasminogen (PLMG) and promotes PLMG conversion to its active form (plasmin) in a dose response in the presence of tissue plasminogen activator. Since plasmin is a key mediator of thrombolysis, our results support the hypothesis that SmGAPDH, a host-interactive tegumental protein that can enhance PLMG activation, could help degrade blood clots around the worms in the vascular microenvironment and thus promote parasite survival in vivoThis article has an associated First Person interview with the first author of the paper.

New insights into the Manila clam - Perkinsus olseni interaction based on gene expression analysis of clam hemocytes and parasite trophozoites through in vitro challenges

The Manila clam (Ruditapes philippinarum) is the bivalve species with the highest global production from both fisheries and aquaculture, but its production is seriously threatened by perkinsosis, a disease caused by the protozoan parasite Perkinsus olseni. To understand the molecular mechanisms underlying R. philippinarum-P. olseni interactions, we analysed the gene expression profiles of in vitro challenged clam hemocytes and P. olseni trophozoites, using two oligo-microarray platforms, one previously validated for R. philippinarum hemocytes and a new one developed and validated in this study for P. olseni. Manila clam hemocytes were in vitro challenged with trophozoites, zoospores, and extracellular products from P. olseni in vitro cultures, while P. olseni trophozoites were in vitro challenged with Manila clam plasma along the same time-series (1 h, 8 h, and 24 h). The hemocytes showed a fast activation of the innate immune response, particularly associated with hemocyte recruitment, in the three types of challenges. Nevertheless, different immune-related pathways were activated in response to the different parasite stages, suggesting specific recognition mechanisms. Furthermore, the analyses provided useful complementary data to previous in vivo challenges, and confirmed the potential of some proposed biomarkers. The combined analysis of gene expression in host and parasite identified several processes in both the clam and P. olseni, such as redox and glucose metabolism, protease activity, apoptosis and iron metabolism, whose modulation suggests cross-talk between parasite and host. This information might be critical to determine the outcome of the infection, thus highlighting potential therapeutic targets. Altogether, the results of this study aid understanding the response and interaction between R. philippinarum and P. olseni, and will contribute to developing effective control strategies for this threatening parasitosis.

Dirofilaria immitis possesses molecules with anticoagulant properties in its excretory/secretory antigens

Dirofilaria immitis is a parasitic nematode that survives in the circulatory system of suitable hosts for many years, causing the most severe thromboembolisms when simultaneous death of adult worms occurs. The two main mechanisms responsible for thrombus formation in mammals are the activation and aggregation of platelets and the generation of fibrin through the coagulation cascade. The aim of this work was to study the anticoagulant potential of excretory/secretory antigens from D. immitis adult worms (DiES) on the coagulation cascade of the host. Anticoagulant and inhibition assays respectively showed that DiES partially alter the coagulation cascade of the host and reduce the activity of the coagulation factor Xa, a key enzyme in the coagulation process. In addition, a D. immitis protein was identified by its similarity to the homologous serpin 6 from Brugia malayi as a possible candidate to form an inhibitory complex with FXa by sodium dodecyl sulfate polyacrylamide gel electrophoresis and mass spectrometry. These results indicate that D. immitis could use the anticoagulant properties of its excretory/secretory antigens to control the formation of blood clots in its immediate intravascular habitat as a survival mechanism.

Molecular characterization of a Trichinella spiralis enolase and its interaction with the host's plasminogen

The binding and activation of host plasminogen (PLG) by worm surface enolases has been verified to participate in parasite invasion, but the role of this processes during Trichinella spiralis infection has not been clarified. Therefore, the expression and immunolocalization of a T. spiralis enolase (TsENO) and its binding activity with PLG were evaluated in this study. Based on the three-dimensional (3D) molecular model of TsENO, the protein interaction between TsENO and human PLG was analysed by the ZDOCK server. The interacting residues were identified after analysis of the protein-protein interface by bioinformatics techniques. The key interacting residues were confirmed by a series of experiments. The qPCR analysis results demonstrated that Ts-eno was transcribed throughout the whole life cycle of T. spiralis. The immunofluorescence assay (IFA) results confirmed that TsENO was distributed on the T. spiralis surface. The binding assays showed that recombinant TsENO (rTsENO) and native TsENO were able to bind PLG. Four lysine residues (90, 289, 291 and 300) of TsENO were considered to be active residues for PLG interaction. The quadruple mutant (Lys90Ala + Lys289Ala + Lys291Ala + Lys300Ala) TsENO, in which the key lysine residues were substituted with alanine (Ala) residues, exhibited a reduction in PLG binding of nearly 50% (45.37%). These results revealed that TsENO has strong binding activity with human PLG. The four lysine residues (90, 289, 291 and 300) of TsENO play an important role in PLG binding and could accelerate PLG activation and invasion of the host's intestinal wall by T. spiralis.

Why Do Intravascular Schistosomes Coat Themselves in Glycolytic Enzymes?

Schistosomes are intravascular parasitic helminths (blood flukes) that infect more than 200 million people globally. Proteomic analysis of the tegument (skin) of these worms has revealed the surprising presence of glycolytic enzymes on the parasite's external surface. Immunolocalization data as well as enzyme activity displayed by live worms confirm that functional glycolytic enzymes are indeed expressed at the host-parasite interface. Since these enzymes are traditionally considered to function intracellularly to drive glycolysis, in an extracellular location they are hypothesized to engage in novel "moonlighting" functions such as immune modulation and blood clot dissolution that promote parasite survival. For instance, several glycolytic enzymes can interact with plasminogen and promote its activation to the thrombolytic plasmin; some can inhibit complement function; some induce B cell proliferation or macrophage apoptosis. Several pathogenic bacteria and protists also express glycolytic enzymes externally, suggesting that moonlighting functions of extracellular glycolytic enzymes can contribute broadly to pathogen virulence. Also see the video abstract here https://youtu.be/njtWZ2y3k_I.

A review of hyperfibrinolysis in cats and dogs

The fibrinolytic system is activated concurrently with coagulation; it regulates haemostasis and prevents thrombosis by restricting clot formation to the area of vascular injury and dismantling the clot as healing occurs. Dysregulation of the fibrinolytic system, which results in hyperfibrinolysis, may manifest as clinically important haemorrhage. Hyperfibrinolysis occurs in cats and dogs secondary to a variety of congenital and acquired disorders. Acquired disorders associated with hyperfibrinolysis, such as trauma, cavitary effusions, liver disease and Angiostrongylus vasorum infection, are commonly encountered in primary care practice. In addition, delayed haemorrhage reported in greyhounds following trauma and routine surgical procedures has been attributed to a hyperfibrinolytic disorder, although this has yet to be characterised. The diagnosis of hyperfibrinolysis is challenging and, until recently, has relied on techniques that are not readily available outside referral hospitals. With the recent development of point-of-care viscoelastic techniques, assessment of fibrinolysis is now possible in referral practice. This will provide the opportunity to target haemorrhage due to hyperfibrinolysis with antifibrinolytic drugs and thereby reduce associated morbidity and mortality. The fibrinolytic system and the conditions associated with increased fibrinolytic activity in cats and dogs are the focus of this review article. In addition, laboratory and point-of-care techniques for assessing hyperfibrinolysis and antifibrinolytic treatment for patients with haemorrhage are reviewed.

Plasminogen-binding proteins as an evasion mechanism of the host's innate immunity in infectious diseases

Pathogens have developed particular strategies to infect and invade their hosts. Amongst these strategies’ figures the modulation of several components of the innate immune system participating in early host defenses, such as the coagulation and complement cascades, as well as the fibrinolytic system. The components of the coagulation cascade and the fibrinolytic system have been proposed to be interfered during host invasion and tissue migration of bacteria, fungi, protozoa, and more recently, helminths. One of the components that has been proposed to facilitate pathogen migration is plasminogen (Plg), a protein found in the host’s plasma, which is activated into plasmin (Plm), a serine protease that degrades fibrin networks and promotes degradation of extracellular matrix (ECM), aiding maintenance of homeostasis. However, pathogens possess Plg-binding proteins that can activate it, therefore taking advantage of the fibrin degradation to facilitate establishment in their hosts. Emergence of Plg-binding proteins appears to have occurred in diverse infectious agents along evolutionary history of host–pathogen relationships. The goal of the present review is to list, summarize, and analyze different examples of Plg-binding proteins used by infectious agents to invade and establish in their hosts. Emphasis was placed on mechanisms used by helminth parasites, particularly taeniid cestodes, where enolase has been identified as a major Plg-binding and activating protein. A new picture is starting to arise about how this glycolytic enzyme could acquire an entirely new role as modulator of the innate immune system in the context of the host–parasite relationship.

Identification and characterization of Taenia solium enolase as a plasminogen-binding protein

The larval stage of Taenia solium (cysticerci) is the causal agent of human and swine cysticercosis. When ingested by the host, T. solium eggs are activated and hatch in the intestine, releasing oncospheres that migrate to various tissues and evolve into cysticerci. Plasminogen (Plg) receptor proteins have been reported to play a role in migration processes for several pathogens. This work is aimed to identify Plg-binding proteins in T. solium cysticerci and determine whether T. solium recombinant enolase (rTsEnoA) is capable of specifically binding and activating human Plg. To identify Plg-binding proteins, a 2D-SDS-PAGE ligand blotting was performed, and recognized spots were identified by MS/MS. Seven proteins from T. solium cysticerci were found capable of binding Plg: fascicilin-1, fasciclin-2, enolase, MAPK, annexin, actin, and cytosolic malate dehydrogenase. To determine whether rTsEnoA binds human Plg, a ligand blotting was performed and the results were confirmed by ELISA both in the presence and absence of εACA, a competitive Plg inhibitor. Finally, rTsEnoA-bound Plg was activated to plasmin in the presence of tPA. To better understand the evolution of enolase isoforms in T. solium, a phylogenetic inference analysis including 75 enolase amino acid sequences was conducted. The origin of flatworm enolase isoforms, except for Eno4, is independent of their vertebrate counterparts. Therefore, herein we propose to designate tapeworm protein isoforms as A, B, C, and 4. In conclusion, recombinant enolase showed a strong plasminogen binding and activating activity in vitro. T. solium enolase could play a role in parasite invasion along with other plasminogen-binding proteins.

Proteomic Analysis of Differentially Expressed Proteins in Intracranial Angiostrongylus cantonensis Larvae in Permissive and Non-Permissive Hosts

Angiostrongylus cantonensis infection can lead to severe neuropathological damage caused by the development of these nematodes in the central nervous system after penetrating the blood-brain barrier. They commonly cause eosinophilic meningitis or meningoencephalitis in non-permissive hosts (e.g., mice). It has been shown that differences exist in the brains of permissive and non-permissive hosts during the larval development of A. cantonensis; however, the mechanism underlying the difference is not completely understood. This study analyzed and characterized the differentially expressed proteins in the intracranial A. cantonensis larvae in rat (ILR) and mouse (ILM) brains by using proteomics. We found that 29 proteins were differentially expressed: 12 of these proteins were highly expressed in ILR, whereas the remaining 17 proteins were highly expressed in ILM. Three protein spots were homologous to the actin-2, actin-1, and disorganized muscle protein 1 (dim-1) of Caenorhabditis elegans. In addition, proteomic analyses revealed that act-1 and act-2 were up-regulated in ILM compared to ILR, whereas dim-1 was down-regulated in ILM. Annotation using gene ontology revealed that act-1, act-2, and dim-1 were mainly associated with adenosine triphosphate (ATP) catabolic processes and ATP binding. Quantitative real-time polymerase chain reaction analyses of act-1 and dim-1 using the first internal transcribed spacers of A. cantonensis 18S ribosomal RNA (rRNA) was consistent with 2-dimensional gel electrophoresis (2-DE) and the sizes of these parasites; ILR was longer and wider than ILM. These results indicate that the differentially expressed proteins dim-1 and act-1 could be related to the development and pathogenicity of A. cantonensis in different hosts.

Plasmatic coagulation and fibrinolysis in healthy and Otostrongylus-affected Northern elephant seals (Mirounga angustirostris)

BACKGROUND

Prepatent Otostrongylus arteritis results in hemorrhagic diathesis in free-ranging Northern elephant seals (Mirounga angustirostris) attributed to aberrant larval migration of the lungworm, Otostrongylus circumlitus. Clinical signs are often nonspecific, including lethargy, anorexia, and blepharospasm, but can progress to spontaneous frank hemorrhage and death within 72 hours of onset. Previously published case reports describe coagulopathy with prolonged PT and APTT, normal to elevated platelet counts, normal antithrombin concentrations, and low concentrations of fibrinogen degradation products. Disseminated intravascular coagulation was proposed as the cause of hemorrhage, but is inconsistent with some of the reported clinicopathologic changes.

OBJECTIVE

The purpose of this study was to compare plasmatic coagulation and fibrinolysis in healthy and Otostrongylus-affected elephant seals, in order to identify potential therapy. We hypothesized that hyperfibrinolysis contributed to hemorrhage in these cases.

METHODS

Citrated plasma samples were collected from 3- to 4-month-old Northern elephant seals in a wildlife rehabilitation hospital. The sampled population included 25 healthy, prerelease seals and 32 clinically ill seals diagnosed with presumptive Otostrongylus arteritis. Twenty-one of the included seals had Otostrongylus infestation confirmed at necropsy. Standard coagulation tests and plasma thromboelastography were performed for a complete assessment of coagulation and fibrinolysis.

RESULTS

Northern elephant seals with definitive Otostrongylus infestation were hypocoagulable and hypofibrinolytic compared to healthy controls.

CONCLUSIONS

Results were most consistent with disseminated intravascular coagulation. Treatment with antifibrinolytic drugs to control hemorrhage may be unrewarding; alternative therapies such as plasma transfusions or coagulation factor concentrates should be investigated.

Hyperfibrinolysis and Hypofibrinogenemia Diagnosed With Rotational Thromboelastometry in Dogs Naturally Infected With Angiostrongylus vasorum

Background

The pathomechanism of Angiostrongylus vasorum infection‐associated bleeding diathesis in dogs is not fully understood.

Objective

To describe rotational thromboelastometry (ROTEM) parameters in dogs naturally infected with A. vasorum and to compare ROTEM parameters between infected dogs with and without clinical signs of bleeding.

Animals

A total of 21 dogs presented between 2013 and 2016.

Methods

Dogs with A. vasorum infection and ROTEM evaluation were retrospectively identified. Thrombocyte counts, ROTEM parameters, clinical signs of bleeding, therapy, and survival to discharge were retrospectively retrieved from patient records and compared between dogs with and without clinical signs of bleeding.

Results

Evaluation by ROTEM showed hyperfibrinolysis in 8 of 12 (67%; 95% CI, 40–86%) dogs with and 1 of 9 (11%; 95% CI, 2–44%) dogs without clinical signs of bleeding (P = .016). Hyperfibrinolysis was associated with severe hypofibrinogenemia in 6 of 10 (60%; 95% CI, 31–83%) of the cases. Hyperfibrinolysis decreased or resolved after treatment with 10–80 mg/kg tranexamic acid. Fresh frozen plasma (range, 14–60 mL/kg) normalized follow‐up fibrinogen function ROTEM (FIBTEM) maximal clot firmness in 6 of 8 dogs (75%; 95% CI, 41–93%). Survival to discharge was 67% (14/21 dogs; 95% CI, 46–83%) and was not different between dogs with and without clinical signs of bleeding (P = .379).

Conclusion and Clinical Importance

Hyperfibrinolysis and hypofibrinogenemia were identified as an important pathomechanism in angiostrongylosis‐associated bleeding in dogs. Hyperfibrinolysis and hypofibrinogenemia were normalized by treatment with tranexamic acid and plasma transfusions, respectively.

PHARMACOKINETIC STUDY OF ORAL ε-AMINOCAPROIC ACID IN THE NORTHERN ELEPHANT SEAL (MIROUNGA ANGUSTIROSTRIS)

ε-Aminocaproic acid (EACA) is a lysine analogue antifibrinolytic drug used to treat bleeding disorders in humans and domestic animals. Its use in zoological medicine is rare, and dosage is anecdotal. One possible application of EACA is to treat bleeding associated with prepatent Otostrongylus arteritis in Northern elephant seals ( Mirounga angustirostris ) presenting to wildlife rehabilitation centers. This study used an in vitro model of hyperfibrinolysis and a thromboelastograph-based assay to estimate the therapeutic plasma concentration of EACA in elephant seals (85 μg/ml, 95% confidence interval = 73.8-96.8 μg/ml). A concurrent pharmacokinetic study of orally administered, single-dose EACA found that doses of 75 and 100 mg/kg achieved therapeutic plasma concentrations (>85 μg/ml), but the drug was rapidly eliminated and remained in the therapeutic range for only 0.4 and 1.5 hr, respectively. Models of repeated oral dosing at 100 mg/kg every 6 hr predict that therapeutic plasma concentration will be maintained for 31.7% (7.6 hr) of a 24-hr period. More frequent dosing would be required to maintain continuous therapeutic concentrations but would be impractical in a wildlife rehabilitation setting. Further pharmacodynamic studies to evaluate the duration of action of EACA in elephant seals and a prospective, placebo-controlled study are needed to determine if EACA is effective in decreasing bleeding associated with prepatent Otostrongylus arteritis and other bleeding disorders in this species.

The Anisakis Transcriptome Provides a Resource for Fundamental and Applied Studies on Allergy-Causing Parasites

Background

Food-borne nematodes of the genus Anisakis are responsible for a wide range of illnesses (= anisakiasis), from self-limiting gastrointestinal forms to severe systemic allergic reactions, which are often misdiagnosed and under-reported. In order to enhance and refine current diagnostic tools for anisakiasis, knowledge of the whole spectrum of parasite molecules transcribed and expressed by this parasite, including those acting as potential allergens, is necessary.

Methodology/Principal Findings

In this study, we employ high-throughput (Illumina) sequencing and bioinformatics to characterise the transcriptomes of two Anisakis species, A. simplex and A. pegreffii, and utilize this resource to compile lists of potential allergens from these parasites. A total of ~65,000,000 reads were generated from cDNA libraries for each species, and assembled into ~34,000 transcripts (= Unigenes); ~18,000 peptides were predicted from each cDNA library and classified based on homology searches, protein motifs and gene ontology and biological pathway mapping. Using comparative analyses with sequence data available in public databases, 36 (A. simplex) and 29 (A. pegreffii) putative allergens were identified, including sequences encoding ‘novel’ Anisakis allergenic proteins (i.e. cyclophilins and ABA-1 domain containing proteins).

Conclusions/Significance

This study represents a first step towards providing the research community with a curated dataset to use as a molecular resource for future investigations of the biology of Anisakis, including molecules putatively acting as allergens, using functional genomics, proteomics and immunological tools. Ultimately, an improved knowledge of the biological functions of these molecules in the parasite, as well as of their immunogenic properties, will assist the development of comprehensive, reliable and robust diagnostic tools.

Nematodes within the genus Anisakis (i.e. A. simplex and A. pegreffii, also known as herring worms) are the causative agents of the fish-borne gastrointestinal illness known as ‘anisakiasis’, with infections resulting in symptoms ranging from mild gastric forms to severe allergic reactions leading to urticaria, gastrointestinal and/or respiratory signs and/or anaphylaxis (‘allergic anisakiasis’). Despite significant advances in knowledge of the pathobiology of allergic anisakiasis, thus far, the exact number and nature of parasite molecules acting as potential allergens are currently unknown; filling this gap is necessary to the development of robust and reliable diagnostics for allergic anisakiasis which, in turn, underpins the implementation of effective therapeutic strategies. Here, we use RNA-Seq and bioinformatics to sequence and annotate the transcriptomes of A. simplex and A. pegreffii, and, as an example application of these resources, mine this data to identify and characterise putative novel parasite allergens based on comparisons with known allergen sequence data from other parasites and other organisms.

Glyceraldehyde 3-phosphate dehydrogenase and galectin from Dirofilaria immitis participate in heartworm disease endarteritis via plasminogen/plasmin system

The interaction between parasitic protozoa and helminths, both in the blood and in tissues and the fibrinolytic system of their hosts is usually considered as a survival parasite mechanism since this system is the physiological route responsible for degrading fibrin clots. The broad-range proteolytic activity of plasmin, the final enzyme of the route, implies that its recruitment by these parasites is an important mechanism that mediates their invasion and establishment in the hosts. However, recent studies have proposed a dual role for plasmin by linking its over-production with pathological mechanisms at vascular level. Most of these studies have been conducted in Dirofilaria immitis, a blood-borne parasite that survives in the pulmonary arteries of its host for years while it produces a chronic inflammatory disease, whose main pathogenic mechanism is the appearance of proliferative endarteritis. Recently, the participation of two proteins from D. immitis, glyceraldehyde 3-phosphate dehydrogenase (DiGAPDH) and galectin (DiGAL), in the activation of the fibrinolytic system of its host has been demonstrated, which has been a priori associated with parasite survival mechanisms. The aim of the present paper was to study the role of plasmin generated by these proteins in the emergence of proliferative endarteritis. An in vitro model of canine endothelial and smooth muscle cells, as well as the two parasitic recombinant proteins were employed. The results show that DiGAPDH and DiGAL stimulate the proliferation and migration of both cell types, as well as the degradation of the extracellular matrix (ECM) via plasminogen (PLG)/plasmin system, being all of these mechanisms related to the appearance of proliferative endarteritis. Due to the high degree of evolutionary conservation of these antigens, these data support the hypothesis of the survival/pathology ambivalence in the interactions between parasites and the fibrinolytic system of their hosts and represent an advance in the knowledge of the mechanisms involved in the emergence of proliferative endarteritis in the cardiopulmonary dirofilariosis (heartworm disease).

Extracellular matrix degradation via enolase/plasminogen interaction: Evidence for a mechanism conserved in Metazoa

BACKGROUND INFORMATION

While enolase is a ubiquitous metalloenzyme involved in the glycolytic pathway, it is also known as a multifunctional protein, since enolases anchored on the outer surface of the plasma membrane are involved in tissue invasion.

RESULTS

We have identified an extracellular enolase (Ae-ENO) produced by the teratocytes, embryonic cells of the insect parasitoid Aphidius ervi. We demonstrate that Ae-ENO, although lacking a signal peptide, accumulates in cytoplasmic vesicles oriented towards the cell membrane. Ae-ENO binds to and activates a plasminogen-like molecule inducing digestion of the host tissue and thereby ensuring successful parasitism.

CONCLUSIONS

These results support the hypothesis that plasminogen-like proteins exist in invertebrates. Interestingly the activation of a plasminogen-like protein is mediated by a mechanisms involving the surface enolase/fibrinolytic system considered, until now, exclusive of vertebrates, and that instead is conserved across species.

SIGNIFICANCE

To our knowledge, this is the first example of enolase mediated Plg-like binding and activation in insect cells, demonstrating the existence of an ECM degradation process via a Plg-like protein in invertebrates.

Plasmin in Parasitic Chronic Infections: Friend or Foe?

Plasmin is the final product of the fibrinolytic system, the physiological mechanism responsible for dissolving fibrin clots. Its broad-range proteolytic activity implies that interaction with fibrinolysis and recruitment of plasmin by blood and tissue parasites is an important mechanism that mediates the invasion and establishment of this kind of pathogen in the hosts. However, recent studies have linked an excess of plasmin generated by this interaction with serious pathological events at the vascular level, including the proliferation and migration of arterial wall cells, inflammation, and degradation of the extracellular matrix. Therefore, we present data that support the need to reconsider the role of plasmin, as well as its benefits or drawbacks, in the context of host-parasite relations.

The Extracellular Vesicles of the Helminth Pathogen, Fasciola hepatica: Biogenesis Pathways and Cargo Molecules Involved in Parasite Pathogenesis

Extracellular vesicles (EVs) released by parasites have important roles in establishing and maintaining infection. Analysis of the soluble and vesicular secretions of adult Fasciola hepatica has established a definitive characterization of the total secretome of this zoonotic parasite. Fasciola secretes at least two subpopulations of EVs that differ according to size, cargo molecules and site of release from the parasite. The larger EVs are released from the specialized cells that line the parasite gastrodermus and contain the zymogen of the 37 kDa cathepsin L peptidase that performs a digestive function. The smaller exosome-like vesicle population originate from multivesicular bodies within the tegumental syncytium and carry many previously described immunomodulatory molecules that could be delivered into host cells. By integrating our proteomics data with recently available transcriptomic data sets we have detailed the pathways involved with EV biogenesis in F. hepatica and propose that the small exosome biogenesis occurs via ESCRT-dependent MVB formation in the tegumental syncytium before being shed from the apical plasma membrane. Furthermore, we found that the molecular “machinery” required for EV biogenesis is constitutively expressed across the intramammalian development stages of the parasite. By contrast, the cargo molecules packaged within the EVs are developmentally regulated, most likely to facilitate the parasites migration through host tissue and to counteract host immune attack.

Surface-displayed glyceraldehyde 3-phosphate dehydrogenase and galectin from Dirofilaria immitis enhance the activation of the fibrinolytic system of the host

Cardiopulmonary dirofilariosis is a cosmopolitan disease caused by Dirofilaria immitis, a filaroid parasite whose adult worms live for years in the vascular system of its host. Previous studies have shown that D. immitis can use their excretory/secretory (ES) and surface antigens to enhance fibrinolysis, which could limit the formation of clots in its surrounding environment. Moreover, several isoforms of the glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and galectin (GAL) were identified in both antigenic extracts as plasminogen-binding proteins. The aim of this work is to study the interaction of the GAPDH and GAL of D. immitis with the fibrinolytic system of the host. This study includes the cloning, sequencing and expression of the recombinant forms of the GAPDH and GAL of D. immitis (rDiGAPDH and rDiGAL) and the analysis of their capacity as plasminogen-binding proteins. The results indicate that rDiGAPDH and rDiGAL are able to bind plasminogen and stimulate plasmin generation by tissue plasminogen activator (tPA). This interaction needs the involvement of lysine residues, many of which are located externally in both proteins as have been shown by the molecular modeling of their secondary structures. In addition, we show that rDiGAPDH and rDiGAL enhance the expression of the urokinase-type plasminogen activator (uPA) on canine endothelial cells in culture and that both proteins are expressed on the surface of D. immitis in close contact with the blood of the host. These data suggest that D. immitis could use the associated surface GAPDH and GAL as physiological plasminogen receptors to shift the fibrinolytic balance towards the generation of plasmin, which might constitute a survival mechanism to avoid the clot formation in its intravascular habitat.

Fibrinolysis and proliferative endarteritis: two related processes in chronic infections? The model of the blood-borne pathogen Dirofilaria immitis

The interaction between blood-borne pathogens and fibrinolysis is one of the most important mechanisms that mediate invasion and the establishment of infectious agents in their hosts. However, overproduction of plasmin (final product of the route) has been related in other contexts to proliferation and migration of the arterial wall cells and degradation of the extracellular matrix. We have recently identified fibrinolysis-activating antigens from Dirofilaria immitis, a blood-borne parasite whose key pathological event (proliferative endarteritis) is produced by similar mechanisms to those indicated above. The objective of this work is to study how two of this antigens [actin (ACT) and fructose-bisphosphate aldolase (FBAL)] highly conserved in pathogens, activate fibrinolysis and to establish a relationship between this activation and the development of proliferative endarteritis during cardiopulmonary dirofilariasis. We demonstrate that both proteins bind plasminogen, enhance plasmin generation, stimulate the expression of the fibrinolytic activators tPA and uPA in endothelial cell cultures and are located on the surface of the worm in contact with the host’s blood. ELISA, western blot and immunofluorescence techniques were employed for this purpose. Additionally, the implication of lysine residues in this interaction was analyzed by bioinformatics. The involvement of plasmin generated by the ACT/FBAL and plasminogen binding in cell proliferation and migration, and degradation of the extracellular matrix were shown in an “in vitro” model of endothelial and smooth muscle cells in culture. The obtained results indicate that ACT and FBAL from D. immitis activate fibrinolysis, which could be used by the parasite like a survival mechanism to avoid the clot formation. However, long-term overproduction of plasmin can trigger pathological events similar to those described in the emergence of proliferative endarteritis. Due to the high degree of evolutionary conservation of these antigens, similar processes may occur in other blood-borne pathogens.

Can the activation of plasminogen/plasmin system of the host by metabolic products of Dirofilaria immitis participate in heartworm disease endarteritis?

Background

Proliferative endarteritis is one of the key pathological mechanisms of cardiopulmonary dirofilariosis, a cosmopolitan parasitosis caused by Dirofilaria immitis affecting dogs and cats around the world. It has been shown that the excretory/secretory antigens from D. immitis adult worms (DiES) bind plasminogen (PLG) and activate fibrinolysis, which can lead to a survival mechanism for the parasite in its intravascular environment. However, overproduction of plasmin (final product of the route) has been related to pathological processes similar to those described in proliferative endarteritis. The aim of this study is to relate the appearance of this pathological condition with the activation of the PLG/plasmin system of the host by DiES.

Methods

Cell proliferation through the crystal violet technique, cell migration by wound healing assay and degradation of the extracellular matrix by measuring collagen degradation and levels of matrix metalloproteinases were studied in an “in vitro” model using canine vascular endothelial and smooth muscle cells. These cells were treated with a mixture of DiES + PLG. Untreated cells, cells only stimulated with DiES or with PLG, or with a mixture of DiES + PLG + εACA (an inhibitor of the PLG-plasmin conversion) were employed as controls. In addition, the effect of DiES on the expression of the fibrinolytic activators tPA and uPA, the inhibitor PAI-1 and the PLG receptor Annexin A2 was analyzed in both types of cultures by western blot.

Results

Plasmin generated by DiES + PLG binding produced a significant increase in the cell proliferation and migration of the endothelial and smooth muscle cells, as well as an increase in the destruction of the extracellular matrix based on a further degradation of Type I Collagen and an increased level of matrix metalloproteinase-2. DiES also induce an increase in the expression of tPA and uPA in endothelial cells in culture, as well as a decrease in the expression of PAI-1 in both types of cells.

Conclusions

Our study reports an interrelationship between plasmin caused by fibrinolysis activation by metabolic products of D. immitis and the appearance of pathological events similar to those described in the emergence of proliferative endarteritis in the cardiopulmonary dirofilariosis.

Moonlighting proteins as virulence factors of pathogenic fungi, parasitic protozoa and multicellular parasites

The delicate balance between eukaryotic pathogens and their human hosts during the initiation and development of infection is a complex process involving many diverse interactions. Different infectious agents, including pathogenic fungi, parasitic protozoa and multicellular parasites, directly interact through their cell surface with epithelial or endothelial cells of the human host as well as various proteinaceous host ligands such as extracellular matrix or plasma proteins. Eukaryotic pathogens possess a number of virulence factors but a relatively recently recognized and particularly interesting group of factors capable of enhancing virulence is the set of so-called 'moonlighting proteins'. This term was coined for a relatively large collection of housekeeping enzymes lacking special targeting motifs that would determine their extracellular localization, but that are often present at the cell surface of pathogen. Several such enzymes with key metabolic functions in glycolysis, the pentose phosphate cycle or other fundamental intracellular processes perform entirely new, non-catalytic roles often associated with adhesion to host ligands. Our current study summarizes some of the current knowledge of interesting moonlighting proteins which play putative or confirmed roles as virulence factors in pathogenic fungi, parasitic protozoa and multicellular parasites.

Proteomic analysis of the somatic and surface compartments from Dirofilaria immitis adult worms

Dirofilaria immitis (hearthworm) is a filarial roundworm transmitted by mosquitoes to different vertebrate hosts (dogs, cats and humans, among others), causing dirofilariosis. The adult worms reside in the pulmonary arteries affecting vessels and tissues and resulting in different pathological manifestations. Worms migrate to the heart and surrounding major vessels in heavy infections. Dirofilariosis can result in serious damage to affected hosts. In the last few years, a re-emergence of the disease driven by the climate change has been pointed out. Very recently, the knowledge at molecular level of this parasite has been extended by the published studies on its genome and transcriptome. Nevertheless, studies on the expression of defined protein sets in different parasite compartments and the corresponding role of those proteins in the host-parasite relationship have been relatively scarce to date. These include the description of the adult worm secretome, and some of the proteins eliciting humoural immune responses and those related with plasminogen binding in secreted and surface extracts of the parasite. Here, we investigate by proteomics the somatic and surface compartments of the D. immitis adult worm, adding new information on protein expression and localization that would facilitate a deeper understanding of the host-parasite relationships in dirofilariosis.

Parasitism in optima forma: exploiting the host fibrinolytic system for invasion

The interaction of pathogenic bacteria with the host fibrinolytic system through the plasminogen molecule has been well documented. It has been shown, using animal models, to be important in invasion into the host and establishment of the infection. From a number of recent observations with parasitic protists and helminths, emerges evidence that also in these organisms the interaction with plasminogen may be important for infection and virulence. A group of molecules that act as plasminogen receptors have been identified in parasites. This group comprises the glycolytic enzymes enolase, glyceraldehyde-3-phosphate dehydrogenase and fructose-1,6-biphosphate aldolase, in common with the plasminogen receptors known in prokaryotic pathogens. The interaction with the fibrinolytic system may arm the parasites with the host protease plasmin, thus helping them to migrate and cross barriers, infect cells and avoid clot formation. In this context, plasminogen receptors on the parasite surface or as secreted molecules, may be considered virulence factors. A possible evolutionary scenario for the recruitment of glycolytic enzymes as plasminogen receptors by widely different pathogens is discussed.