Immunolocalization and developmental expression patterns of two cathepsin B proteases (AC-cathB-1, -2) of Angiostrongylus cantonensis

The trypsin inhibitor-like domain is required for a serine protease inhibitor of Haemonchus contortus to inhibit host coagulation

Haemonchus contortus, a blood-feeding nematode, inhibits blood coagulation at the site of infection to facilitate blood-sucking and digesting for successful parasitism. However, the mechanism underlying anti-coagulation at the host-parasite interface is largely unknown. In the current study, Hc-spi-i8, which has two greatly different transcripts named Hc-spi-i8a and Hc-spi-i8b, respectively, was described. Hc-SPI-I8A was a serine protease inhibitor containing a trypsin inhibitor-like cysteine rich (TIL) domain, while Hc-SPI-I8B was not. Hc-SPI-I8A/B were primarily expressed in the hypodermis, intestines and gonads in the parasitic stages of H. contortus. Hc-SPI-I8A interacted with Ovis aries TSP1-containing protein (OaTSP1CP), which was determined by yeast two-hybrid, co-immunoprecipitation (Co-IP), pull down and co-localization experiments. The blood clotting time contributed by the TIL domain was prolonged by Hc-SPI-I8A. Hc-SPI-I8A is most likely interfering in the extrinsic coagulation cascade by interacting with OaTSP1CP through its TIL domain and intrinsic coagulation cascade by an unknown mechanism. These findings depict a crucial point in the host-parasite interaction during H. contortus colonization, which should contribute to drug discovery and vaccine development in fighting against this important parasite worldwide.

Differential proteolytic activity in Anisakis simplex s.s. and Anisakis pegreffii, two sibling species from the complex Anisakis simplex s.l., major etiological agents of anisakiasis

Proteolytic activity was studied in two sibling species of Anisakis (Nematoda: Anisakidae), A. simplex s.s. and A. pegreffii, throughout their in vitro development from third larval stage (L3) from the host fish (L3-0h) to fourth larval stage (L4) obtained in culture. Proteases have a significant role in the lifecycle of the parasite and in the pathogen-host relationship. Proteolytic activity peaks were detected at pH 6.0 and 8.5. Protease activity was detected in all the developmental stages of the two species studied at both pH values. These pH values were used for assaying with specific inhibitors which permitted the determination of metalloprotease activity, and, to a lesser extent, that of serine and cysteine protease. Aspartic protease activity was only detected at pH 6.0. At this pH, L4 larvae showed higher proteolytic activity than L3 larvae in both species (p < 0.001), the majority of activity being due to metalloproteases and aspartic proteases, which could be related to nutrition, especially the latter, as occurs in invertebrates. At pH 8.5, proteolytic activity was higher in A. simplex s.s. than in A. pegreffii (p < 0.01). At this pH, the majority of activity was due to metalloproteases in all developmental phases of both species, although, in L3-0h, the activity of these proteases was significantly higher (p < 0.03) in A. simplex s.s. than in A. pegreffii. This could be related to the greater invasive capacity of the former. Serine proteases have frequently been implicated in the invasive capacity and pathogenicity of some parasites. This may be related to the significantly higher activity (p ≤ 0.05) of serine protease in all the larval stages of A. simplex studied at pH 6.0. Thus, there are interspecific differences in proteases that have been related to pathogenesis in nematodes. These differences could thus be contributing to the previously reported differences in pathogenicity between these two Anisakis species.

Activity profiling of peptidases in Angiostrongylus costaricensis first-stage larvae and adult worms

BACKGROUND

Angiostrongylus costaricensis is a relatively uncharacterized nematode that causes abdominal angiostrongyliasis in Latin America, a human parasitic disease. Currently, no effective pharmacological treatment for angiostrongyliasis exists. Peptidases are known to be druggable targets for a variety of diseases and are essential for several biological processes in parasites. Therefore, this study aimed to systematically characterize the peptidase activity of A. costaricensis in different developmental stages of this parasitic nematode.

METHODOLOGY/PRINCIPAL FINDINGS

A library of diverse tetradecapeptides was incubated with cellular lysates from adult worms and from first-stage larvae (L1) and cleaved peptide products were identified by mass spectrometry. Lysates were also treated with class specific peptidase inhibitors to determine which enzyme class was responsible for the proteolytic activity. Peptidase activity from the four major mechanistic classes (aspartic, metallo, serine and cysteine) were detected in adult worm lysate, whereas aspartic, metallo and serine-peptidases were found in the larval lysates. In addition, the substrate specificity profile was found to vary at different pH values.

CONCLUSIONS/SIGNIFICANCE

The proteolytic activities in adult worm and L1 lysates were characterized using a highly diversified library of peptide substrates and the activity was validated using a selection of fluorescent substrates. Taken together, peptidase signatures for different developmental stages of this parasite has improved our understanding of the disease pathogenesis and may be useful as potential drug targets or vaccine candidates.

Cysteine proteases as digestive enzymes in parasitic helminths

We briefly review cysteine proteases (orthologs of mammalian cathepsins B, L, F, and C) that are expressed in flatworm and nematode parasites. Emphasis is placed on enzyme activities that have been functionally characterized, are associated with the parasite gut, and putatively contribute to degrading host proteins to absorbable nutrients [1–4]. Often, gut proteases are expressed as multigene families, as is the case with Fasciola [5] and Haemonchus [6], presumably expanding the range of substrates that can be degraded, not least during parasite migration through host tissues [5]. The application of the free-living planarian and Caenorhabditis elegans as investigative models for parasite cysteine proteases is discussed. Finally, because of their central nutritive contribution, targeting the component gut proteases with small-molecule chemical inhibitors and understanding their utility as vaccine candidates are active areas of research [7].

Host-location behavior of the tea green leafhopper Empoasca vitis Göthe (Hemiptera: Cicadellidae): olfactory and visual effects on their orientation

The tea green leafhopper, Empoasca vitis Göthe, is one of the most serious pests in tea growing areas. This study investigated the roles played by olfaction and vision in host orientation behavior. The compound eye of E. vitis was found to be a photopic eye; few olfactory sensilla were found on the antennae, while abundant gustatory sensilla were recorded on the mouthparts. Three opsin genes (EV_LWop, EV_UVop, EV_Bop) were isolated and found to be mainly expressed in the compound eye compared with other parts of the body. Immunolocalization indicated that the opsins mainly located in the different regions of rhabdom. The transcription levels of EV_LWop, EV_Bop and EV_UVop were reduced by 77.3, 70.0 and 40.0%, respectively, by RNA interference induced by being fed a special RNA-rich diet for 6 days. The rate of tropism to host color was effectively impaired by 67.6 and 29.5% in the dsEV_LWop and dsEV_Bop treatment groups, but there was no significant change in the dsEV_UVop group. The determination of the cause of the tropism indicated that odors from the host over long distances were unable to attract E. vitis and were only detected when the insects were close to the host. The developed compound eye of E. vitis plays a leading role in host location, and the long-wavelength opsin significantly affects the tropism to host color; the lack of olfactory sensilla results in long-distance odors not being able to be detected until the insect is near to the host-plant. The understanding of these behavioral mechanisms, especially the importance of opsin genes is expected to be useful for pest management.

Angiostrongylus cantonensis: a review of its distribution, molecular biology and clinical significance as a human pathogen

Angiostrongylus cantonensis is a metastrongyloid nematode found widely in the Asia-Pacific region, and the aetiological agent of angiostrongyliasis; a disease characterized by eosinophilic meningitis. Rattus rats are definitive hosts of A. cantonensis, while intermediate hosts include terrestrial and aquatic molluscs. Humans are dead-end hosts that usually become infected upon ingestion of infected molluscs. A presumptive diagnosis is often made based on clinical features, a history of mollusc consumption, eosinophilic pleocytosis in cerebral spinal fluid, and advanced imaging such as computed tomography. Serological tests are available for angiostrongyliasis, though many tests are still under development. While there is no treatment consensus, therapy often includes a combination of anthelmintics and corticosteroids. Angiostrongyliasis is relatively rare, but is often associated with morbidity and sometimes mortality. Recent reports suggest the parasites' range is increasing, leading to fatalities in regions previously considered Angiostrongylus-free, and sometimes, delayed diagnosis in newly invaded regions. Increased awareness of angiostrongyliasis would facilitate rapid diagnosis and improved clinical outcomes. This paper summarizes knowledge on the parasites' life cycle, clinical aspects and epidemiology. The molecular biology of Angiostrongylus spp. is also discussed. Attention is paid to the significance of angiostrongyliasis in Australia, given the recent severe cases reported from the Sydney region.

Pepsin is a positive regulator of Ac-cathB-2 involved in the rat gut penetration of Angiostrongylus cantonensis

Background

Angiostrongyliasis caused by the rat lungworm, Angiostrongylus cantonensis (A. cantonensis), has globally spread from the traditional epidemic areas. The small intestine is the site where the third-stage larvae (L3) of this worm entered the host body, and parasite proteases are involved in this process. Ac-cathB-2, a cathepsin B-like cysteine of A. cantonensis, was formerly isolated from the insoluble part of fragmentised Escherichia coli without activity. The unplanned low activity of prokaryotic expression proteins and difficulties in genetic modification hindered understanding the function of this protein.

Methods

The recombinant Ac-cathB-2 was expressed and harvested from 293 T cells and the enzymatic property and the effects of processing on the activity of the recombinant protease were investigated in vitro. The expression of Ac-cathB-2 in response to external stimulation was assessed, and the function of this protease during host gut penetration was observed by using antiserum for inhibition.

Results

Of the life-cycle stages studied, L3 expressed the highest level of Ac-cathB-2 gene and released the corresponding gene product from the body. The expression of this gene was rapidly upregulated after incubating L3 in small intestine homogenate of rat. Recombinant Ac-cathB-2 was harvested from 293 T cell culture medium. This protease was activated by pepsin-HCl and the enabled Ac-cathB-2 could subsequently digest laminin and fibronectin readily. Moreover, the small intestine isolated from rat was disrupted after incubating with the activated Ac-cathB-2, resulting in the detachment of epithelial cells. Antiserum treatment inhibited the hydrolytic ability of recombinant Ac-cathB-2 by 82.7 %, and also reduced the tissue penetration of activated L3 by 41.2 %. Additionally, pre-incubation of L3 with artificial gastric acid increased the number of penetrating larvae by 53.2 %, and this alteration could be partly blocked by antiserum treatment.

Conclusion

We believe that Ac-cathB-2 from A. cantonensis might help the worm to penetrate the rat gut, because the protease was able to degrade the tissue components of host. Nevertheless, our results further indicated that host pepsin played a beneficial role in this process by cleaving Ac-cathB-2 for activation. Thus, Ac-cathB-2 may probably represent an important target for the control of A. cantonensis infection.

Angiostrongylus cantonensis cathepsin B-like protease (Ac-cathB-1) is involved in host gut penetration

Although the global spread of the emerging zoonosis, human angiostrongyliasis, has attracted increasing attention, understanding of specific gene function has been impeded by the inaccessibility of genetic manipulation of the pathogen nematode causing this disease, Angiostrongylus cantonensis. Many parasitic proteases play key roles in host-parasite interactions, but those of A. cantonensis are always expressed as the inactive form in prokaryotic expression systems, thereby impeding functional studies. Hence, a lentiviral system that drives secreted expression of target genes fused to a Myc-His tag was used to obtain recombinant Ac-cathB-1 with biological activity. Although this class of proteases was always reported to function in nutrition and immune evasion in parasitic nematodes, recombinant Ac-cathB-1 was capable of hydrolysis of fibronectin and laminin as well as the extracellular matrix of IEC-6 monolayer, so that the intercellular space of the IEC-6 monolayer increased 5.15 times as compared to the control, while the shape of the adherent cells partly rounded up. This suggests a probable role for this protease in intestinal epithelial penetration. The inhibition of Ac-cathB-1 enzymatic activity with antiserum partly suppressed larval penetration ability in the isolated intestine. Thus, an effective system for heterologous expression of parasite proteases is presented for studying gene function in A. cantonensis; and Ac-cathB-1 was related to larval penetration ability in the host small intestine.

Enolase of Angiostrongylus cantonensis: more likely a structural component?

The cloned enolase gene of Angiostrongylus cantonensis (AcEno) comprised 1,667 bp and encoded a peptide with 434 amino acid residues which lacked of a signal peptide but contained a transmembrane region, indicating that AcEno tends to be a structural component (intracellular or membrane protein). The real-time PCR revealed a meaningful difference in the expression level of AcEno in varied development stages. By immunolocalization, native AcEno was detected mainly in the cytoplasm in most tissues, such as parietal muscle, genital tracts, nerve ring, and alimentary canal where the energy consumption is high, but not as expected on the cuticle and hypodermis layer of the nematode. This suggests that the AcEno may be involved in a host of other biological functions, rather than a receptor of plasminogen or a component of excretory-secretory antigen. In addition, AcEno expressed alike in the nucleus, indicating that AcEno also involved in regulating the continuous growth and development of A. cantonensis in hosts. Despite of living in the vasculature at a certain stage of life cycle, AcEno was not localized in the outer surface of L3 and adults, indicating that A. cantonensis may have other virulence and immune evasion mechanisms.