Plasmin in Parasitic Chronic Infections: Friend or Foe?

C-Terminal Lysine Residue of Pneumococcal Triosephosphate Isomerase Contributes to Its Binding to Host Plasminogen

The main causative agent of pneumonia, Streptococcus pneumoniae, is also responsible for invasive diseases. S. pneumoniae recruits human plasminogen for the invasion and colonization of host tissues. We previously discovered that S. pneumoniae triosephosphate isomerase (TpiA), an enzyme involved in intracellular metabolism that is essential for survival, is released extracellularly to bind human plasminogen and facilitate its activation. Epsilon-aminocaproic acid, a lysine analogue, inhibits this binding, suggesting that the lysine residues in TpiA are involved in plasminogen binding. In this study, we generated site-directed mutant recombinants in which the lysine residue in TpiA was replaced with alanine and analyzed their binding activities to human plasminogen. Results from blot analysis, enzyme-linked immunosorbent assay, and surface plasmon resonance assay revealed that the lysine residue at the C-terminus of TpiA is primarily involved in binding to human plasminogen. Furthermore, we found that TpiA binding to plasminogen through its C-terminal lysine residue was required for the promotion of plasmin activation by activating factors.

Molecular Characterization of the Interplay between Fasciola hepatica Juveniles and Laminin as a Mechanism to Adhere to and Break through the Host Intestinal Wall

Fasciola hepatica is the main causative agent of fasciolosis, a zoonotic parasitic disease of growing public health concern. F. hepatica metacercariae are ingested by the host and excyst in the intestine, thereby releasing the newly excysted juveniles (FhNEJ), which traverse the gut wall and migrate towards the biliary ducts. Since blocking F. hepatica development is challenging after crossing of the intestinal wall, targeting this first step of migration might result in increased therapeutic success. The intestinal extracellular matrix (ECM) is constituted by a network of structural proteins, including laminin (LM) and fibronectin (FN), that provide mechanical support while acting as physical barrier against intestinal pathogens. Here, we employed ELISA and immunofluorescent assays to test for the presence of LM- and FN-binding proteins on a tegument-enriched antigenic fraction of FhNEJ, and further determined their identity by two-dimensional electrophoresis coupled to mass spectrometry. Additionally, we performed enzymatic assays that revealed for the first time the capability of the juvenile-specific cathepsin L3 to degrade LM, and that LM degradation by FhNEJ proteins is further potentiated in the presence of host plasminogen. Finally, a proteomic analysis showed that the interaction with LM triggers protein changes in FhNEJ that may be relevant for parasite growth and adaptation inside the mammalian host. Altogether, our study provides valuable insights into the molecular interplay between FhNEJ and the intestinal ECM, which may lead to the identification of targetable candidates for the development of more effective control strategies against fasciolosis.

Fasciola hepatica juveniles interact with the host fibrinolytic system as a potential early-stage invasion mechanism

BACKGROUND

The trematode Fasciola hepatica is the most widespread causative agent of fasciolosis, a parasitic disease that mainly affects humans and ruminants worldwide. During F. hepatica infection, newly excysted juveniles (FhNEJ) emerge in the duodenum of the mammalian host and migrate towards their definitive location, the intra-hepatic biliary ducts. Understanding how F. hepatica traverses the intestinal wall and migrates towards the liver is pivotal for the development of more successful strategies against fasciolosis. The central enzyme of the mammalian fibrinolytic system is plasmin, a serine protease whose functions are exploited by a number of parasite species owing to its broad spectrum of substrates, including components of tissue extracellular matrices. The aim of the present work is to understand whether FhNEJ co-opt the functions of their host fibrinolytic system as a mechanism to facilitate trans-intestinal migration.

METHODOLOGY/PRINCIPAL FINDINGS

A tegument-enriched antigenic extract of FhNEJ (FhNEJ-Teg) was obtained in vitro, and its capability to bind the zymogen plasminogen (PLG) and enhance its conversion to the active protease, plasmin, were analyzed by a combination of enzyme-linked immunosorbent, chromogenic and immunofluorescence assays. Additionally, PLG-binding proteins in FhNEJ-Teg were identified by bidimensional electrophoresis coupled to mass spectrometry analysis, and the interactions were validated using FhNEJ recombinant proteins.

CONCLUSIONS/SIGNIFICANCE

Our results show that FhNEJ-Teg contains proteins that bind PLG and stimulate its activation to plasmin, which could facilitate the traversal of the intestinal wall by FhNEJ and contribute to the successful establishment of the parasite within its mammalian host. Altogether, our findings contribute to a better understanding of host-parasite relationships during early fasciolosis and may be exploited from a pharmacological and/or immunological perspective for the development of treatment and control strategies against this global disease.

Proteomic analysis of the excretory-secretory products from Strongyloides venezuelensis infective larvae: new insights for the immunodiagnosis of human strongyloidiasis

Serodiagnosis of human strongyloidiasis is a practical alternative to parasitological methods due to its high sensitivity. However, cross-reactivity with other helminth infections limits its utility, and this problem is due to the use of homologous or heterologous somatic extracts of the parasite as an antigen source. Excretory-secretory (E/S) products from Strongyloides infective larvae can be used to improve the serodiagnosis. The combined use of western blot and proteomics became an interesting strategy to identify immunological markers for the serodiagnosis of strongyloidiasis. The present study describes the proteomic analysis of the antigenic components from E/S products of S. venezuelensis infective larvae that were recognized by IgG antibodies from patients with strongyloidiasis. Our results showed that IgG antibodies from patients with strongyloidiasis recognized between 15 and 16 antigenic bands in the E/S products from S. venezuelensis that were incubated in PBS or in RPMI culture medium, respectively. Overall, antigenic bands of low and high molecular weight were more specific than those of intermediate molecular weight, which were cross-reactive. A 36-kDa antigenic band was 93% sensitive and 100% specific (a probably arginine kinase of 37 kDa), while other antigenic bands were highly sensitive but low specific. Proteomic analysis revealed differences between the protein profiles from E/S-RPMI and E/S-PBS since only one-third of all proteins identified were common in both types of E/S products. Bioinformatic analysis showed that more than 50% of the proteins from E/S products are secreted within extracellular vesicles and only a small percentage of them are actually released by the classical secretory pathway. Several components from the E/S products were identified as plasminogen-binding proteins, probably used as an immune evasion mechanism. The data provided here provide valuable information to increase understanding of E/S products from S. venezuelensis infective larvae. This may help us to find new targets for the immunodiagnosis of human strongyloidiasis.

Interaction of helminth parasites with the haemostatic system of their vertebrate hosts: a scoping review

Helminth parasitoses are among the most prevalent health issues worldwide. Their control depends largely on unravelling host–parasite interactions, including parasitic exploitation of the host haemostatic system. The present study undertakes a scoping review of the research carried out in this field with the aim of unifying and updating concepts. Multiple keywords combined with Boolean operators were employed to design the literature search strategy. Two online databases were used to identify original peer-reviewed articles written in English and published before 1st January 2020 describing molecular interactions between helminth parasites and the host haemostatic system. Relevant data from the selected sources of evidence were extracted and analysed. Ninety-six publications reporting 259 interactions were selected. Fifty-three proteins belonging to 32 species of helminth parasites were involved in interactions with components of the host haemostatic system. Many of these proteins from both parasite and host were conserved among the different interactions identified. Most of these interactions were related to the inhibition of the coagulation system and the activation of fibrinolysis. This was associated mainly with a potential of parasites to reduce the formation of blood clots in the host and attributed to biological processes, such as parasite nutrition, survival, invasion, evasion and migration or the appearance of pathological mechanisms in the host. A wide range of helminth parasites have developed similar strategies to exploit the haemostatic system of their hosts, which could be regarded as an evolutionary conserved mechanism that could confer benefits to parasites in terms of survival and establishment in their vertebrate hosts.

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.

Host-Parasite Relationships in Porcine Ascariosis: Anticoagulant Potential of the Third Larval Stage of Ascaris suum as a Possible Survival Mechanism

Simple Summary

Ascaris suum parasitises pigs all over the world causing a disease responsible for producing reductions in weight gains and damages to several organs of the infected animals that incur huge economic losses for the swine industry. While adult worms of this parasite are located in the small intestine of the host, their larval stages migrate through the bloodstream as an evolutionary advantageous strategy within a hostile environment that confronts host responses such as blood clots formation. The aim of this work is to study the ability of A. suum larvae to inhibit blood coagulation as a possible mechanism to control blood clots formation and facilitate their migration. The results showed that these larvae inhibited host blood coagulation and possessed molecules similar to those responsible for inhibiting blood coagulation in pigs. The anticoagulant effect of A. suum larvae could constitute a potential survival mechanism for the parasite. Therefore, developing new control strategies directed at this and similar processes could avoid A. suum larval migration and the establishment of adult worms in their definitive location, which is necessary to confront the damages and economic losses produced by this parasitosis.

Abstract

In order to evade the response of their hosts, helminth parasites have evolved precise and highly regulated mechanisms, including migration strategies of the larval stages. In regard to porcine ascariosis caused by Ascaris suum, its infective third-stage larvae (AsL3) undergo a complex migratory route through the bloodstream of their host before establishing in the small intestine to reach maturation. Despite the benefits attributed to this migration, blood clots formation could compromise larvae survival. The aim of this work was to study the interaction between the cuticle and excretory/secretory antigens of AsL3 and the host coagulation cascade. Larvae were obtained after incubating and hatching A. suum eggs, after which the antigenic extracts were produced. Their ability to disrupt the coagulation cascade was studied using anticoagulation and chromogenic assays, and techniques based on electrophoresis. The obtained results showed that both antigenic extracts possessed anticoagulant potential, being able to inhibit the intrinsic, extrinsic and/or common pathways of the blood coagulation cascade as well as the activated factor X. Moreover, three A. suum serpin proteins were identified as candidates to inhibit this host coagulation factor. To the best of our knowledge, this study shows, for the first time, the anticoagulant potential of the infective larvae of A. suum, which could be used by the parasite as a mechanism to facilitate its invasion and survival in the host.

The fibrinolytic system enables the onset of Plasmodium infection in the mosquito vector and the mammalian host

Plasmodium parasites must migrate across proteinaceous matrices to infect the mosquito and vertebrate hosts. Plasmin, a mammalian serine protease, degrades extracellular matrix proteins allowing cell migration through tissues. We report that Plasmodium gametes recruit human plasminogen to their surface where it is processed into plasmin by corecruited plasminogen activators. Inhibition of plasminogen activation arrests parasite development early during sexual reproduction, before ookinete formation. We show that increased fibrinogen and fibrin in the blood bolus, which are natural substrates of plasmin, inversely correlate with parasite infectivity of the mosquito. Furthermore, we show that sporozoites, the parasite form transmitted by the mosquito to humans, also bind plasminogen and plasminogen activators on their surface, where plasminogen is activated into plasmin. Surface-bound plasmin promotes sporozoite transmission by facilitating parasite migration across the extracellular matrices of the dermis and of the liver. The fibrinolytic system is a potential target to hamper Plasmodium transmission.

Au-Cu@PANI Alloy Core Shells for Aerobic Fibrin Degradation under Visible Light Exposure

Fibrin plays a critical role in wound healing and hemostasis, yet it is also the main case of cardiovascular diseases and thrombosis. Here, we show the unique design of Au-Cu@PANI alloy core-shell rods for fibrin clot degradation. Microscopic (transmission electron microscopy (TEM), scanning transmission electron microscopy-energy-dispersive X-ray (STEM-EDX)) and structural characterizations (powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS)) of the Au-Cu@PANI hybrid material reveal the formation of Au-Cu heterogeneous alloy core rods (aspect ratio = 3.7) with thin Cu₂O and PANI shells that create a positive surface charge (ζ-potential = +22 mV). This architecture is supported by the survey XPS spectrum showing the presence of Cu 2p, N 1s, and C 1s features with binding energies of 934.8, 399.7, and 284.8 eV, respectively. Upon photolysis (λ ≥ 495 or 590 nm), these hybrid composite nanorods provide sufficient excited-state redox potential to generate reactive oxygen species (ROS) for degradation of model fibrin clots within 5-7 h. Detailed scanning electron microscopy (SEM) analysis of the fibrin network shows significant morphology modification including formation of large voids and strand termini, indicating degradation of fibrin protofibril by Au-Cu@PANI. The dye 1,3-diphenylisobenzofuran (DPBF) used to detect the presence of ¹O₂ shows a 27% bleaching of the absorption at λ = 418 nm within 75 min of irradiation of an aqueous Au-Cu@PANI solution in air. Moreover, electron paramagnetic resonance (EPR) spin-trapping experiments reveal a hyperfine-coupled triplet signature at room temperature with intensities 1:1:1: and g-value = 2.0057, characteristic of the reaction between the spin probe 4-Oxo-TEMP and ¹O₂ during irradiation. Controlled ¹O₂ scavenging experiments by NaN₃ show 82% reduction in the spin-trapped EPR signal area. Both DPBF bleaching and EPR spin trapping indicate that in situ generated ¹O₂ is responsible for fibrin strand scission. This unique nanomaterial function via use of ubiquitous oxygen as a reagent could open creative avenues for future in vivo biomedical applications to treat fibrin clot diseases.

Insights into Fasciola hepatica Juveniles: Crossing the Fasciolosis Rubicon

Unraveling the molecular interactions governing the first contact between parasite and host tissues is of paramount importance to the development of effective control strategies against parasites. In fasciolosis, a foodborne trematodiasis caused mainly by Fasciola hepatica, these early interactions occur between the juvenile worm and the host intestinal wall a few hours after ingestion of metacercariae, the infectious stage of the parasite. However, research on these early events is still scarce and the majority of studies have focused on the adult worm. Here, we review current knowledge on the biology and biochemistry of F. hepatica juveniles and their molecular relationships with the host tissues and identify the research needs and gaps to be covered in the future.

Human Plasminogen Exacerbates Clostridioides difficile Enteric Disease and Alters the Spore Surface

BACKGROUND & AIMS

The protease plasmin is an important wound healing factor, but it is not clear how it affects gastrointestinal infection-mediated damage, such as that resulting from Clostridioides difficile. We investigated the role of plasmin in C difficile-associated disease. This bacterium produces a spore form that is required for infection, so we also investigated the effects of plasmin on spores.

METHODS

C57BL/6J mice expressing the precursor to plasmin, the zymogen human plasminogen (hPLG), or infused with hPLG were infected with C difficile, and disease progression was monitored. Gut tissues were collected, and cytokine production and tissue damage were analyzed by using proteomic and cytokine arrays. Antibodies that inhibit either hPLG activation or plasmin activity were developed and structurally characterized, and their effects were tested in mice. Spores were isolated from infected patients or mice and visualized using super-resolution microscopy; the functional consequences of hPLG binding to spores were determined.

RESULTS

hPLG localized to the toxin-damaged gut, resulting in immune dysregulation with an increased abundance of cytokines (such as interleukin [IL] 1A, IL1B, IL3, IL10, IL12B, MCP1, MP1A, MP1B, GCSF, GMCSF, KC, TIMP-1), tissue degradation, and reduced survival. Administration of antibodies that inhibit plasminogen activation reduced disease severity in mice. C difficile spores bound specifically to hPLG and active plasmin degraded their surface, facilitating rapid germination.

CONCLUSIONS

We found that hPLG is recruited to the damaged gut, exacerbating C difficile disease in mice. hPLG binds to C difficile spores, and, upon activation to plasmin, remodels the spore surface, facilitating rapid spore germination. Inhibitors of plasminogen activation might be developed for treatment of C difficile or other infection-mediated gastrointestinal diseases.

Fibrinolysis and COVID-19: A plasmin paradox

The COVID-19 pandemic has provided many challenges in the field of thrombosis and hemostasis. Among these is a novel form of coagulopathy that includes exceptionally high levels of D-dimer. D-dimer is a marker of poor prognosis, but does this also imply a causal relationship? These spectacularly raised D-dimer levels may actually signify the failing attempt of the fibrinolytic system to remove fibrin and necrotic tissue from the lung parenchyma, being consumed or overwhelmed in the process. Indeed, recent studies suggest that increasing fibrinolytic activity might offer hope for patients with critical disease and severe respiratory failure. However, the fibrinolytic system can also be harnessed by coronavirus to promote infectivity and where antifibrinolytic measures would also seem appropriate. Hence, there is a clinical paradox where plasmin formation can be either deleterious or beneficial in COVID-19, but not at the same time. Hence, it all comes down to timing.

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.

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.

Profiling Transcriptional Regulation and Functional Roles of Schistosoma mansoni c-Jun N-Terminal Kinase

Mitogen-activated protein kinases (MAPKs) play a regulatory role and influence various biological activities, such as cell proliferation, differentiation, and survival. Our group has demonstrated through functional studies that Schistosoma mansoni c-Jun N-terminal kinase (SmJNK) MAPK is involved in the parasite's development, reproduction, and survival. SmJNK can, therefore, be considered a potential target for the development of new drugs. Considering the importance of SmJNK in S. mansoni maturation, we aimed at understanding of SmJNK regulated signaling pathways in the parasite, correlating expression data with S. mansoni development. To better understand the role of SmJNK in S. mansoni intravertebrate host life stages, RNA interference knockdown was performed in adult worms and in schistosomula larval stage. SmJNK knocked-down in adult worms showed a decrease in oviposition and no significant alteration in their movement. RNASeq libraries of SmJNK knockdown schistosomula were sequenced. A total of 495 differentially expressed genes were observed in the SmJNK knockdown parasites, of which 373 were down-regulated and 122 up-regulated. Among the down-regulated genes, we found transcripts related to protein folding, purine nucleotide metabolism, the structural composition of ribosomes and cytoskeleton. Genes coding for proteins that bind to nucleic acids and proteins involved in the phagosome and spliceosome pathways were enriched. Additionally, we found that SmJNK and Smp38 MAPK signaling pathways converge regulating the expression of a large set of genes. C. elegans orthologous genes were enriched for genes related to sterility and oocyte maturation, corroborating the observed phenotype alteration. This work allowed an in-depth analysis of the SmJNK signaling pathway, elucidating gene targets of regulation and functional roles of this critical kinase for parasite maturation.

Angiogenic response in an in vitro model of dog microvascular endothelial cells stimulated with antigenic extracts from Dirofilaria immitis adult worms

BACKGROUND

Angiogenesis can occur under pathological conditions when stimuli such as inflammation, vascular obstruction or hypoxia exist. These stimuli are present in cardiopulmonary dirofilariosis (Dirofilaria immitis). The aim of this study was to analyze the capacity of D. immitis antigens to modify the expression of angiogenic factors and trigger the formation of pseudocapillaries (tube-like structures) in an in vitro model of endothelial cells.

METHODS

The expression of VEGF-A, sFlt, mEndoglin and sEndoglin in cultures of canine microvascular endothelial cells stimulated with extract of adult worms of D. immitis obtained from an untreated dog (DiSA) and from a dog treated for 15 days with doxycycline (tDiSA), was determined by using commercial kits. The capacity of pseudocapillary formation was evaluated analyzing cell connections and cell groups in Matrigel cell cultures stimulated with DiSA and tDiSA. In both cases non-stimulated cultures were used as controls.

RESULTS

First, we demonstrated that worms obtained from the dog treated with doxycycline showed a significantly lower amount of Wolbachia (less than 60%) than worms removed from the untreated dog. Only DiSA was able to significantly increase the expression of the proangiogenic factor VEGF-A in the endotelial cells cultures. None of the D. immitis extracts modified the expression of sFlt. tDiSA extract was able to modify the expression of the endoglins, significantly decreasing the expression of the pro-angiogenic mEndoglin and increasing the anti-angiogenic sEndoglin. The formation of pseudocapillaries was negatively influenced by tDiSA, which reduced the organization and number of cellular connections.

CONCLUSIONS

The ability of antigens from adult D. immitis worms to modify the expression of pro and anti-angiogenic factors in endotelial cell cultures was demonstrated, as well as the trend to form pseudocapillaries in vitro. The capacity of stimulation may be linked to the amount of Wolbachia present in the antigenic extracts.

Numerous Fasciola plasminogen-binding proteins may underlie blood-brain barrier leakage and explain neurological disorder complexity and heterogeneity in the acute and chronic phases of human fascioliasis

Human fascioliasis is a worldwide, pathogenic food-borne trematodiasis. Impressive clinical pictures comprising puzzling polymorphisms, manifestation multifocality, disease evolution changes, sequelae and mortality, have been reported in patients presenting with neurological, meningeal, neuropsychic and ocular disorders caused at distance by flukes infecting the liver. Proteomic and mass spectrometry analyses of the Fasciola hepatica excretome/secretome identified numerous, several new, plasminogen-binding proteins enhancing plasmin generation. This may underlie blood-brain barrier leakage whether by many simultaneously migrating, small-sized juvenile flukes in the acute phase, or by breakage of encapsulating formations triggered by single worm tracks in the chronic phase. Blood-brain barrier leakages may subsequently occur due to a fibrinolytic system-dependent mechanism involving plasmin-dependent generation of the proinflammatory peptide bradykinin and activation of bradykinin B2 receptors, after different plasminogen-binding protein agglomeration waves. Interactions between diverse parasitic situations and non-imbalancing fibrinolysis system alterations are for the first time proposed that explain the complexity, heterogeneity and timely variations of neurological disorders. Additionally, inflammation and dilation of blood vessels may be due to contact system-dependent generation bradykinin. This baseline allows for search of indicators to detect neurological risk in fascioliasis patients and experimental work on antifibrinolytic treatments or B2 receptor antagonists for preventing blood-brain barrier leakage.

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.

The Complexity of Zoonotic Filariasis Episystem and Its Consequences: A Multidisciplinary View

Vector-borne transmitted helminthic zoonosis affects the health and economy of both developing and developed countries. The concept of episystem includes the set of biological, environmental, and epidemiological elements of these diseases in defined geographic and temporal scales. Dirofilariasis caused by different species of the genus Dirofilaria is a disease affecting domestic and wild canines and felines and man, transmitted by different species of culicid mosquitoes. This complexity is increased because Dirofilaria species harbor intracellular symbiont Wolbachia bacteriae, which play a key role in the embryogenesis and development of dirofilariae and in the inflammatory pathology of the disease. In addition, the vector transmission makes the dirofilariasis susceptible to the influence of the climate and its variations. The present review addresses the analysis of dirofilariasis from the point of view of the episystem, analyzing the complex network of interactions established between biological components, climate, and factors related to human activity, as well as the different problems they pose. The progress of knowledge on human and animal dirofilariasis is largely due to the multidisciplinary approach. Nevertheless, different aspects of the disease need to continue being investigated and cooperation between countries and specialists involved should be intensified.

Complete Molecular and Immunoprotective Characterization of Babesia microti Enolase

The apicomplexan Babesia microti is the primary causative agent of human babesiosis, one of the most broadly distributed tick-borne diseases worldwide. B. microti undergoes a complex lifecycle within both the mammalian host and the tick vector, and employs several different specific molecular mechanisms to enter host cells. Enolase, the key glycolytic enzyme in intracellular glucose metabolism, can also be expressed on the parasite’s outer surface, binds to human plasminogen, and coordinates apicomplexan parasite invasion of host cells, however, it lacks sorting sequences or lipoprotein anchor sites. In the present study, we isolated the coding gene of B. microti enolase (BmEno), expressed it within E. coli and purified the recombinant BmEno protein (rBmEno). Consequently, we confirmed cytoplasmic and surface localization of BmEno via immunofluorescence, and demonstrated that rBmEno catalyzes the dehydration of 2-phospho-D-glycerate to phosphoenolpyruvate. Moreover, our results showed that rBmEno binds to human plasminogen, and that the lysine analog ε-aminocaproic acid significantly inhibited this binding. Furthermore plasminogen bound to rBmEno converts to active plasmin. Additionally, actively immunizing mice with rBmEno could evoke a partial protective immunity against B. microti infection following challenge. In conclusion, B. microti enolase is a multifunctional cytoplasmic protein which is also expressed at the parasitic outer surface, facilitates binding to host plasminogen, and could partially protect hosts against parasite infection.

Schistosoma bovis-host interplay: Proteomics for knowing and acting

Schistosoma bovis is a parasite of ruminants that causes significant economic losses to farmers throughout Africa, Southwestern Asia and the Mediterranean. Additionally, recent studies have reported its zoonotic potential through the formation of S. bovis×Schistosoma haematobium hybrids. As observed in the Schistosoma species infecting humans, it is assumed that S. bovis has also evolved host regulatory molecules that ensure its long-term survival in the bloodstream of its host. Since these molecules could be potential targets for the development of new drugs and anti-schistosome vaccines, their identification and functional characterization were undertaken. With this aim in mind, the molecular interface between S. bovis and its vertebrate host was subjected to a series of proteomic studies, which started with the analysis of the proteomes of the S. bovis moieties exposed to the host, namely, the excretory/secretory products and the tegument surface. Thus, a wealth of novel molecular information of S. bovis was obtained, which in turn allowed the identification of several parasite proteins with fibrinolytic and anticoagulant activities that could be used by S. bovis to regulate the host defensive systems. Following on, the host interface was investigated by studying the proteome of the host vascular endothelium surface at two points along the infection: in the lung vessels during the schistosomula migration and in the portal vein after the parasites have reached adulthood and sexual maturity. These studies have provided original data regarding the proteomes of the endothelial cell surface of pulmonary vasculature and portal vein in S. bovis-infected animals, and have shown significant changes in these proteomes associated with infection. This review compiles current information and the analyses of all the proteomic data from S. bovis and the S. bovis-host interface, including the molecular and functional characterization of S. bovis proteins that were found to participate in the regulation of the host coagulation and fibrinolysis systems.

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).