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

Molecular characterization of a novel serine proteinase from Trichinella spiralis and its participation in larval invasion of gut epithelium

BACKGROUND

A novel serine proteinase of Trichinells spiralis (TsSPc) has been identified in the excretion/secretion (ES) antigens, but its role in larval invasion is unclear. The aim of this study was to clone and express TsSPc, identify its biological and biochemical characteristics, and investigate its role on larval invasion of gut epithelium during T. spiralis infection.

METHODOLOGY/PRINCIPAL FINDINGS

TsSPc has a functional domain of serine proteinase, and its tertiary structure consists of three amino acid residues (His88, Asp139 and Ser229) forming a pocket like functional domain. Recombinant TsSPc (rTsSPc) was expressed and purified. The rTsSPc has good immunogenicity. On Western blot analysis, rTsSPc was recognized by infection serum and anti-rTsSPc serum, natural TsSPc in crude and ES antigens was identified by anti-rTsSPc serum. The results of qPCR, Western blot and indirect immunofluorescence test (IIFT) showed that TsSPc was expressed at diverse stage worms, and mainly localized at cuticle, stichosome and intrauterine embryos of this nematode. The rTsSPc had enzymatic activity of native serine protease, which hydrolyzed the substrate BAEE, casein and collagen I. After site directed mutation of enzymatic active sites of TsSPc, its antigenicity did not change but the enzyme activity was fully lost. rTsSPc specifically bound to intestinal epithelium cells (IECs) and the binding sites were mainly localized in cell membrane and cytoplasm. rTsSPc accelerated larval invasion of IECs, whereas anti-rTsSPc antibodies and TsSPc-specific dsRNA obviously hindered larval invasion.

CONCLUSIONS

TsSPc was a surface and secretory proteinase of the parasite, participated in larval invasion of gut epithelium, and may be considered as a candidate vaccine target molecule against Trichinella intrusion and infection.

Proteases secreted by Trichinella spiralis intestinal infective larvae damage the junctions of the intestinal epithelial cell monolayer and mediate larval invasion

The intestinal epithelium is the first natural barrier against Trichinella spiralis larval invasion, but the mechanism of larval invasion of the gut epithelium is not fully elucidated. The aim of this study was to investigate whether the excretory/secretory proteins (ESPs) of T. spiralis intestinal infective larvae (IIL) degrade tight junction (TJ) proteins, to assess the main ESP proteases hydrolysing TJ proteins using various enzyme inhibitors and to define the key invasive factors in IIL invasion of the gut epithelium. The results of immunofluorescence, Western blot and Transwell assays showed that serine proteases and cysteine proteases in the ESPs played main roles in hydrolysing occludin, claudin-1 and E-cad and upregulating claudin-2 expression. Challenge infection results showed that IIL expulsion from the gut at 12 hpi was significantly higher in mice which were infected with muscle larvae (ML) treated with a single inhibitor (PMSF, E-64, 1,10-Phe or pepstatin) or various mixtures containing PMSF and E-64 than in mice in the PBS group or the groups treated with an inhibitor mixture not containing PMSF and E-64 (P < 0.0001). At 6 days post-infection, mice which were infected with ML treated with PMSF, E-64, 1,10-Phe or pepstatin exhibited 56.30, 64.91, 26.42 and 31.85% reductions in intestinal adult worms compared to mice in the PBS group (P < 0.0001). The results indicate that serine proteases and cysteine proteases play key roles in T. spiralis IIL invasion, growth and survival in the host and that they may be main candidate target molecules for vaccines against larval invasion and development.

Temperature-induced reorganisation of Schistocephalus solidus (Cestoda) proteome during the transition to the warm-blooded host

The protein composition of the cestode Schistocephalus solidus was measured in an experiment simulating the trophic transmission of the parasite from a cold-blooded to a warm-blooded host. The first hour of host colonisation was studied in a model experiment, in which sticklebacks Gasterosteus aculeatus infected with S. solidus were heated at 40°C for 1 h. As a result, a decrease in the content of one tegument protein was detected in the plerocercoids of S. solidus. Sexual maturation of the parasites was initiated in an experiment where S. solidus larvae were taken from fish and cultured in vitro at 40°C for 48 h. Temperature-independent changes in the parasite proteome were investigated by incubating plerocercoids at 22°C for 48 h in culture medium. Analysis of the proteome allowed us to distinguish the temperature-induced genes of S. solidus, as well as to specify the molecular markers of the plerocercoid and adult worms. The main conclusion of the study is that the key enzymes of long-term metabolic changes (glycogen consumption, protein production, etc.) in parasites during colonisation of a warm-blooded host are induced by temperature.

Functional characterization of a glutathione S-transferase in Trichinella spiralis invasion, development and reproduction

The purpose of this study was to determine the biological function of a Trichinella spiralis glutathione S-transferase (TsGST) in larval invasion and development by RNA interference (RNAi). The TsGST-specific siRNA 366 was transfected into T. spiralis muscle larvae (ML) via electroporation. At 1 day following transfection, the larval TsGST mRNA and protein expressions were reduced by 40.09 and 65.22 % (P < 0.05), respectively. The enzymatic activity of natural TsGST in siRNA-transfected ML was also suppressed by 45% compared with PBS group (P < 0.05). Silencing of the TsGST significantly inhibited the ability of larvae to invade intestinal epithelium cells (IECs) and isolated intestine. After challenge with siRNA-366-treated ML, the infected mice exhibited a 62.82% reduction of intestinal adult worms, and 65.03 % reduction of muscle larvae compared to the PBS group. Besides, the length of adults, newborn larvae and muscle larvae was significantly shorter than that of control siRNA and PBS group; the female fecundity of siRNA 366 group was lower than those of control siRNA and PBS group (P <  0.05). The results revealed that the specific RNAi significantly reduced the expression and enzymatic activity of TsGST, inhibited the larval invasive and developmental capacity, and impaired the female fecundity. The results further confirmed that TsGST plays a crucial role in the T. spiralis life cycle and it might be a potential molecular target for anti-Trichinella vaccines.

Interaction of a Trichinella spiralis cathepsin B with enterocytes promotes the larval intrusion into the cells

Cathepsin B is one member of cysteine protease family and widely distributed in organisms, it plays an important function in parasite penetrating, migrating, molting and immune escaping. The aim of this work was to investigate whether exist interaction between a Trichinella spiralis cathepsin B (TsCB) and mouse intestinal epithelium cells (IECs), and its influence in the process of larva cell invasion. The results of ELISA, indirect immunofluorescence assay (IIFA), confocal microscopy and Far western blotting showed that there was a strong specific binding of rTsCB and IEC proteins, and the binding positions were located in cytoplasm and nuclei of IECs. The results of the in vitro larva penetration test revealed that rTsCB facilitated the larva invasion of IECs, whereas anti-rTsCB antibodies impeded partially the larva intrusion of enterocytes, this promotive or inhibitory roles were dose-dependent of rTsCB or anti-rTsCB antibodies. Silencing TsCB by siRNA mediated RNA interference reduced the TsCB expression in T. spiralis larvae, and markedly inhibited the larva penetration of enterocytes. The results indicated that TsCB binding to IECs promoted larva penetration of host's enteral epithelia, and it is a promising molecular target against intestinal invasive stages of T. spiralis.

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].

Comparative transcriptomic analysis of two important life stages of Angiostrongylus cantonensis: fifth-stage larvae and female adults

The mechanisms involved in the fast growth of Angiostrongylus cantonensis from fifth-stage larvae (L5) to female adults and how L5 breaks through the blood-brain barrier in a permissive host remain unclear. In this work, we compared the transcriptomes of these two life stages to identify the main factors involved in the rapid growth and transition to adulthood. RNA samples from the two stages were sequenced and assembled de novo. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses of 1,346 differentially expressed genes between L5 and female adults was then undertaken. Based on a combination of analytical results and developmental characteristics, we suggest that A. cantonensis synthesizes a large amount of cuticle in L5 to allow body dilatation in the rapid growth period. Products that are degraded via the lysosomal pathway may provide sufficient raw materials for cuticle production. In addition, metallopeptidases may play a key role in parasite penetration of the blood-brain barrier during migration from the brain. Overall, these results indicate that the profiles of each transcriptome are tailored to the need for survival in each developmental stage.

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.