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

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.

Serum proteome of dogs with chronic enteropathy

BACKGROUND

Chronic enteropathy (CE) is common in dogs and can occur with multiple etiologies including food-responsive enteropathy (FRE) and idiopathic inflammatory bowel disease (IBD).

HYPOTHESIS/OBJECTIVE

To study the protein profile and pathway differences among dogs with FRE, IBD, and healthy controls using serum proteome analysis.

ANIMALS

Nine CE dogs with signs of gastrointestinal disease and histologically confirmed chronic inflammatory enteropathy and 16 healthy controls.

METHODS

A cross-sectional study with cases recruited from 2 veterinary hospitals between May 2019 and November 2020 was performed. Serum samples were analyzed using mass spectrometry-based proteomic techniques.

RESULTS

Proteomic profiles showed marked variation in relative protein abundances. Forty-five proteins were significantly (P ≤ .01) differentially expressed among the dogs with CE and controls with ≥2-fold change in abundance. The fold change of dogs with IBD normalized to controls was more pronounced for the majority of proteins than that seen in the dogs with FRE normalized to control dogs. Proteins involving reactive oxygen species, cytokine activation, acute phase response signaling, and lipid metabolism were altered in dogs with CE.

CONCLUSIONS AND CLINICAL IMPORTANCE

Cytokine alterations, acute phase response signaling, and lipid metabolism are likely involved in pathogenesis of CE. Although there are insufficient current data to justify the use of proteomic biomarkers for assessment of CE in dogs, our study identifies potential candidates.

Prospects of Using High-Throughput Proteomics to Underpin the Discovery of Animal Host-Nematode Interactions

Parasitic nematodes impose a significant public health burden, and cause major economic losses to agriculture worldwide. Due to the widespread of anthelmintic resistance and lack of effective vaccines for most nematode species, there is an urgent need to discover novel therapeutic and vaccine targets, informed through an understanding of host-parasite interactions. Proteomics, underpinned by genomics, enables the global characterisation proteins expressed in a particular cell type, tissue and organism, and provides a key to insights at the host-parasite interface using advanced high-throughput mass spectrometry-based proteomic technologies. Here, we (i) review current mass-spectrometry-based proteomic methods, with an emphasis on a high-throughput 'bottom-up' approach; (ii) summarise recent progress in the proteomics of parasitic nematodes of animals, with a focus on molecules inferred to be involved in host-parasite interactions; and (iii) discuss future research directions that could enhance our knowledge and understanding of the molecular interplay between nematodes and host animals, in order to work toward new, improved methods for the treatment, diagnosis and control of nematodiases.

The Secretome of Filarial Nematodes and Its Role in Host-Parasite Interactions and Pathogenicity in Onchocerciasis-Associated Epilepsy

Filarial nematodes secrete bioactive molecules which are of interest as potential mediators for manipulating host biology, as they are readily available at the host-parasite interface. The adult parasites can survive for years in the mammalian host, due to their successful modulation of the host immune system and most of these immunomodulatory strategies are based on soluble mediators excreted by the parasite. The secretome of filarial nematodes is a key player in both infection and pathology, making them an interesting target for further investigation. This review summarises the current knowledge regarding the components of the excretory-secretory products (ESPs) of filarial parasites and their bioactive functions in the human host. In addition, the pathogenic potential of the identified components, which are mostly proteins, in the pathophysiology of onchocerciasis-associated epilepsy is discussed.

A possible relationship between Thromboxane B2 and Leukotriene B4 and the encapsulation of Dirofilaria repens worms in human subcutaneous dirofilariasis

Human subcutaneous dirofilariosis has several clinical presentations. Many cases present as subcutaneous nodules, as a consequence of a local inflammatory reaction that encapsulates and destroys the worms. In addition, there are cases in which migrating worms located in the ocular area remain unencapsulated. In the present work, the levels of two pro-inflammatory eicosanoids, thromboxane B2 (TxB2) and leukotriene B4 (LTB4) are analysed by commercial Enzime-Linked immunosorbent assay (ELISA) in serum samples from 43 individuals, 28 diagnosed as having subcutaneous dirofilariasis presenting a subcutaneous nodule, five diagnosed as having dirofilariasis, in which the worms remained unencapsulated in the periphery of the eye, and ten healthy individuals living in a non-endemic area, used as controls. The worms were surgically removed, identifying Dirofilaria repens as the causative agent in all cases, by Polymerase Chain Reaction (PCR). Individuals with nodules showed significantly higher levels of TxB2 and LTB4 than healthy controls, whereas significant differences in LTB4 levels were observed between individuals with unencapsulated worms and healthy controls. It is speculated that the absence of LTB4 may contribute to the fact that worms remain unencapsulated as a part of immune evasion mechanisms.

Proteomic analysis of excretory-secretory products from young adults of Angiostrongylus cantonensis

BACKGROUND

Angiostrongyliasis is caused by the nematode Angiostrongylus cantonensis and can lead to eosinophilic meningitis and meningoencephalitis in humans. The young adult worms play central pathogenic roles in the central nervous system (CNS); however, the underlying mechanism is unclear. Excretory-secretory products (ESPs) are good investigation targets for studying the relationship between a host and its parasite.

OBJECTIVES

We aimed to profile, identify, and characterise the proteins in the ESPs of A. cantonensis young adults.

METHODS

The ESPs of young adult worms were collected from culture medium after incubation ranging from 24 to 96 h. Proteomic and bioinformatics analyses were performed to characterise the ESPs.

FINDINGS

A total of 51 spots were identified, and the highly expressed proteins included two protein disulphide isomerases, one calreticulin, and three uncharacterised proteins. Subsequently, approximately 254 proteins were identified in the ESPs of A. cantonensis young adults via liquid chromatography-mass spectrometry (LC-MS/MS) analysis, and these were further classified according to their characteristics and biological functions. Finally, we identified the immunoreactive proteins from a reference map of ESPs from A. cantonensis young adults. Approximately eight proteins were identified, including a protein disulphide isomerase, a putative aspartic protease, annexin, and five uncharacterised proteins. The study established and identified protein reference maps for the ESPs of A. cantonensis young adults.

MAIN CONCLUSIONS

The identified proteins may be potential targets for the development of diagnostic or therapeutic agents for human angiostrongyliasis.

Fatty-binding protein and galectin of Baylisascaris schroederi: Prokaryotic expression and preliminary evaluation of serodiagnostic potential

Baylisascaris schroederi is a common parasite of captive giant pandas. The diagnosis of this ascariasis is normally carried out by a sedimentation-floatation method or PCR to detect eggs in feces, but neither method is suitable for early diagnosis. Fatty acid-binding protein (FABP) and galectin (GAL) exist in various animals and participate in important biology of parasites. Because of their good immunogenicity, they are seen as potential antigens for the diagnosis of parasitic diseases. In this study, we cloned and expressed recombinant FABP and GAL from B. schroederi (rBs-FABP and rBs-GAL) and developed indirect enzyme-linked immunosorbent assays (ELISAs) to evaluate their potential for diagnosing ascariasis in giant pandas. Immunolocalization showed that Bs-FABP and Bs-GAL were widely distributed in adult worms. The ELISA based on rBs-FABP showed sensitivity of 95.8% (23/24) and specificity of 100% (12/12), and that based on rBs-GAL had sensitivity of 91.7% (22/24) and specificity of 100% (12/12).

Signaling in Parasitic Nematodes: Physicochemical Communication Between Host and Parasite and Endogenous Molecular Transduction Pathways Governing Worm Development and Survival

Signaling or communication between host and parasite may occur over relatively long ranges to enable host finding and acquisition by infective parasitic nematode larvae. Innate behaviors in infective larvae transmitted from the soil that enhance the likelihood of host contact, such as negative geotaxis and hypermotility, are likely mediated by mechanoreception and neuromuscular signaling. Host cues such as vibration of the substratum, elevated temperature, exhaled CO2, and other volatile odorants are perceived by mechanosensory and chemosensory neurons of the amphidial complex. Beyond this, the molecular systems that transduce these external cues within the worm are unknown at this time. Overall, the signal transduction mechanisms that regulate switching between dauer and continuous reproductive development in Caenorhabditis elegans, and doubtless other free-living nematodes, have provided a useful framework for testing hypotheses about how the morphogenesis and development of infective parasitic nematode larvae and the lifespan of adult parasites are regulated. In C. elegans, four major signal transduction pathways, G protein-coupled receptor signaling, insulin/insulin-like growth factor signaling, TGFβ-like signaling and steroid-nuclear hormone receptor signaling govern the switch between dauer and continuous development and regulate adult lifespan. Parasitic nematodes appear to have conserved the functions of G-protein-coupled signaling, insulin-like signaling and steroid-nuclear hormone receptor signaling to regulate larval development before and during the infective process. By contrast, TGFβ-like signaling appears to have been adapted for some other function, perhaps modulation of the host immune response. Of the three signal transduction pathways that appear to regulate development in parasitic nematodes, steroid-nuclear hormone signaling is the most straightforward to manipulate with administered small molecules and may form the basis of new chemotherapeutic strategies. Signaling between parasites and their hosts' immune systems also occurs and serves to modulate these responses to allow chronic infection and down regulate acute inflammatory responses. Knowledge of the precise nature of this signaling may form the basis of immunological interventions to protect against parasitism or related lesions and to alleviate inflammatory diseases of various etiologies.

Perusal of parasitic nematode 'omics in the post-genomic era

The advent of high-throughput, next-generation sequencing methods combined with advances in computational biology and bioinformatics have greatly accelerated discovery within biomedical research. This "post-genomics" era has ushered in powerful approaches allowing one to quantify RNA transcript and protein abundance for every gene in the genome - often for multiple conditions. Herein, we chronicle how the post-genomics era has advanced our overall understanding of parasitic nematodes through transcriptomics and proteomics and highlight some of the important advances made in each major nematode clade. We primarily focus on organisms relevant to human health, given that nematode infections significantly impact disability-adjusted life years (DALY) scores within the developing world, but we also discuss organisms of veterinary importance as well as those used as laboratory models. As such, we envision that this review will serve as a comprehensive resource for those seeking a better understanding of basic parasitic nematode biology as well as those interested in targets for vaccination and pharmacological intervention.

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.

Molecular and biochemical characterisation of abomasal nematode parasites Teladorsagia circumcincta and Haemonchus contortus phosphofructokinases and their recognition by the immune host

Full length cDNAs encoding phosphofructokinase (PFK) were cloned from Teladorsagia circumcincta (TcPFK) and Haemonchus contortus (HcPFK). TcPFK (2361 bp) and HcPFK (2367 bp) cDNA encoded 787 and 789 amino acid proteins respectively. The predicted amino acid sequences showed 98% similarity with each other and 70% with a Caenorhabditis elegans PFK. Substrate binding sites were completely conserved in both proteins. Soluble N-terminal His-tagged PFK proteins were expressed in Escherichia coli strain BL21, purified and characterised. The recombinant TcPFK and HcPFK had very similar kinetic properties: the pH optima were pH 7.0, Km for fructose 6-phosphate was 0.50 ± 0.01 and 0.55 ± 0.01 mM respectively when higher (inhibiting concentration, 0.3 mM) ATP concentration was used and the curve was sigmoidal. The Vmax for TcPFK and HcPFK were 1110 ± 16 and 910 ± 10 nM min(-1 )mg(-1) protein respectively. Lower ATP concentration (non-inhibiting, 0.01 mM) did not change the Vmax for TcPFK and HcPFK (890 ± 10 and 860 ± 12 nM min(-1 )mg(-1) protein) but the substrate affinity doubled and Km for fructose 6-phosphate were 0.20 ± 0.05 and 0.25 ± 0.01 mM respectively. Recognition of TcPFK and HcPFK by mucosal and serum antibodies in nematode exposed animals demonstrates antigenicity and suggests involvement in the host response to nematode infection.