Glyceroneogenesis: an unexpected metabolic pathway for glutamine in Schistosoma mansoni sporocysts

Deciphering the mechanism of anhydrobiosis in the entomopathogenic nematode Heterorhabditis indica through comparative transcriptomics

The entomopathogenic nematode, Heterorhabditis indica, is a popular biocontrol agent of high commercial significance. It possesses tremendous genetic architecture to survive desiccation stress by undergoing anhydrobiosis to increase its lifespan-an attribute exploited in the formulation technology. The comparative transcriptome of unstressed and anhydrobiotic H. indica revealed several previously concealed metabolic events crucial for adapting towards the moisture stress. During the induction of anhydrobiosis in the infective juveniles (IJ), 1584 transcripts were upregulated and 340 downregulated. As a strategy towards anhydrobiotic survival, the IJ showed activation of several genes critical to antioxidant defense, detoxification pathways, signal transduction, unfolded protein response and molecular chaperones and ubiquitin-proteasome system. Differential expression of several genes involved in gluconeogenesis - β-oxidation of fatty acids, glyoxylate pathway; glyceroneogenesis; fatty acid biosynthesis; amino-acid metabolism - shikimate pathway, sachharopine pathway, kyneurine pathway, lysine biosynthesis; one-carbon metabolism-polyamine pathway, transsulfuration pathway, folate cycle, methionine cycle, nucleotide biosynthesis; mevalonate pathway; and glyceraldehyde-3-phosphate dehydrogenase were also observed. We report the role of shikimate pathway, sachharopine pathway and glyceroneogenesis in anhydrobiotes, and seven classes of repeat proteins, specifically in H. indica for the first time. These results provide insights into anhydrobiotic survival strategies which can be utilized to strengthen the development of novel formulations with enhanced and sustained shelf-life.

Drug effects on metabolic profiles of Schistosoma mansoni adult male parasites detected by 1H-NMR spectroscopy

Schistosomiasis is one of the most devastating neglected tropical parasitic diseases caused by trematodes of the genus Schistosoma. Praziquantel (PZQ) is today the only drug used in humans and animals for the treatment of schistosomiasis but unfortunately it is poorly effective on larval and juvenile stages of the parasite. Therefore, it is urgent the discovery of new drug targets and compounds. We have recently showed that the anti-anginal drug perhexiline maleate (PHX) is very active on multiple developmental stages of Schistosoma mansoni in vitro. It is well known that PHX impacts the lipid metabolism in mammals, but the final target on schistosomes still remains unknown. The aim of this study was to evaluate the ability of ¹H nuclear magnetic resonance (NMR) spectroscopy in revealing metabolic perturbations due to PHX treatment of S. mansoni adult male worms. The effects of PHX were compared with the ones induced by vehicle and gambogic acid, in order to detect different metabolic profiles and specificity of the PHX action. Remarkably a list of metabolites associated to PHX-treatment was identified with enrichment in several connected metabolic pathways including also the Kennedy pathway mediating the glycerophospholipid metabolism. Our study represents the first ¹H-NMR metabolomic approach to characterize the response of S. mansoni to drug treatment. The obtained “metabolic fingerprint” associated to PHX treatment could represent a strategy for displaying cellular metabolic changes for any given drug and to compare compounds targeting similar or distinct biochemical pathways.

Schistosomiasis is a chronic and debilitating neglected tropical parasitic disease caused by the helminth Schistosoma. The control and treatment of the disease rely almost exclusively on praziquantel (PZQ), poorly effective on some developmental stage of the parasite. Identification of novel targets and drugs is required. The aim of this study was to use a ¹H-NMR metabolomic approach to characterize the response of Schistosoma mansoni to perhexiline maleate (PHX), a multi-stage schistosomicidal drug previously investigated by our group. Remarkably we identified a metabolic signature specifically associated to drug-treatment in adult male parasites. This approach could contribute to the identification of novel targets and biochemical pathways implicated in parasite development and survival.

Molecular cloning, expression, and immunolocalization of the NAD(+)-dependent glycerol 3-phosphate dehydrogenase (GPD) from Clonorchis sinensis

Glycerol 3-phosphate dehydrogenase (GPD) plays an important role in the energy metabolism and nutrition metabolism. In order to know about the biological functions of GPD of Clonorchis sinensis (C. sinensis), we identified a complete gene coding GPD from C. sinensis metacercaria cDNA library. This novel cDNA sequence contains 1,056 bp with a putative open reading frame of 351 amino acids and shares 74% identity with GPD from Schistosoma mansoni. Recombinant CsGPD was expressed and purified from Escherichia coli BL21 (DE3). Western blot analysis displayed that recombinant CsGPD can be recognized by anti-CsGPD serum and C. sinensis-infected serum. RT-PCR and immunolocalization analysis confirmed that GPD expressed both at the stage of adult worm and metacercaria of C. sinensis and immunolocated at the tegument of adult worm, tegument and tegumentary cells of metacercaria. Our current study has paved the way for the further researches about the biological functions involved in the growth of C. sinensis.

Excretory/secretory proteome of the adult stage of Echinostoma caproni

The excretory/secretory proteome of Echinostoma caproni (Trematoda: Echinostomatidae) adults collected from experimentally infected mice was investigated using a proteomic approach. We performed a shot-gun liquid chromatography/tandem mass spectrometry for the separation and identification of tryptic peptides from the excretory/secretory products of E. caproni adult worms. Database search was performed using MASCOT search engine (Matrix-Science) and ProteinPilot software v2.0 (Applied Biosystems). A total of 39 parasite proteins were accurately identified. Strikingly, metabolic enzymes, and particularly glycolytic enzymes, constituted the largest protein family in the excretory/secretory proteome of E. caproni adult worms. Moreover, representative proteins involved in parasite structure, response against stress, chaperones, calcium-binding, and signal transduction were also identified. This work extends our knowledge of host-parasite relationships in the E. caproni-rodent model that is extensively used to analyze the factors determining the intestinal helminth rejection. Consequently, information on many proteins may be useful to better understand the molecular basis that determines the survival of this parasite in the definitive host.

Molecular cloning and characterisation of SmSLK, a novel Ste20-like kinase in Schistosoma mansoni

Serine/threonine kinases of the Ste20 group play important roles in various cellular functions such as growth, apoptosis and morphogenesis. This family includes p21-Activated Kinases (PAKs) and Germinal Center Kinases (GCKs) families which contain their kinase domain in the C-terminal and N-terminal position, respectively. Here, we report the characterisation of a novel Ste20-like kinase (SLK) in the helminth parasite Schistosoma mansoni (SmSLK). SmSLK belongs to the GCK subfamily and contains a conserved N-terminal Ste20-like catalytic domain and C-terminal coiled-coil structures homologous to mammalian Lymphocyte Oriented Kinase (LOK) and SLK kinases and described as regulatory domains in these proteins. Gene assembly was performed using S. mansoni sequences available from genomic databases and indicated that SmSLK is composed of 18 exons and present in one copy in the S. mansoni genome. RT-PCR experiments demonstrated an alternative splicing of SmSLK in the exon 9 encoding the hinge region between kinase and coiled-coil domains of SmSLK and showed the expression of both transcript isoforms (SmSLK and SmSLK-S in which exon 9 is deleted) in all the S. mansoni parasite stages. Most of the Ste20-related proteins are active kinases known to regulate mitogen-activated protein kinase (MAPK) cascades. We demonstrated the kinase activity of SmSLK and SmSLK-S and their capacity to activate the MAPK/Jun N-terminal kinase (JNK) pathway in human embryonic kidney (HEK) cells as well as in Xenopus oocytes. Immunofluorescence studies indicated that SmSLK proteins were abundant in the tegument of adult schistosomes. Therefore, these results indicate that SmSLK is a new member of the GCK protein family that could participate in the regulation of MAPK cascade activation during host-parasite interactions.

Molecular analysis of SmFes, a tyrosine kinase of Schistosoma mansoni orthologous to the members of the Fes/Fps/Fer family

A novel protein tyrosine kinase (PTK) was identified in Schistosoma mansoni and designated SmFes. SmFes exhibits the characteristic features of Fes/Fps/Fer (fes, feline sarcoma; fps, Fujinami poultry sarcoma; fer, fes related) PTKs, containing three coiled-coil regions, an SH2 (Src-homology-2) and a TK (tyrosine kinase catalytic) domain signature. SmFes is the first gene from the Fes/Fps/Fer family identified in S. mansoni, and is a single copy gene. Phylogenetic analyses revealed that SmFes is most closely related to its invertebrate orthologues. The assembly of the SmFes cDNA and genomic sequences indicated the presence of 18 introns in SmFes. Comparison of its genomic structure with those of human Fps/Fes and Drosophila Fps indicates that intron positions are conserved within the region encoding the kinase domain. Analysis of partial cDNA clones showed the presence of a 9 bp insertion at the 3' end of exon 10, producing two different cDNA populations, pointed as an alternative splicing event. In addition, an allele of SmFes containing a 15 bp insertion was observed in the genomic sequence. Quantitative RT-PCR indicated that the overall transcription level of SmFes is rather low in all parasite developmental stages. Moreover, SmFes mRNA levels decrease progressively after cercarial transformation, consistent with a role for the corresponding protein in the early stages of infection.

Evaluation of the effect of oxamniquine, praziquantel and a combination of both drugs on the intramolluscan phase of Schistosoma mansoni

The activity of oxamniquine (OXA), praziquantel (PZQ), and a combination of both drugs was evaluated at the intramolluscan phase of Schistosoma mansoni. Biomphalaria glabrata snails infected with S. mansoni were treated with 500 mg/kg OXA, 1000 mg/kg PZQ or with 250 mg/kg OXA and 500 mg/kg PZQ, in association, at the pre-patent and patent phases of infection. The results showed that either treatments with OXA or PZQ, alone, at the pre-patent period, delayed the parasite's development, increasing the pre-patent period by approximately 10 days. At the same pre-patent period, treatment with a combination of OXA/PZQ delayed the parasite's development even more, extending the pre-patent period up to 56 days. At the patent period, treatment with OXA and PZQ, alone, interrupted cercarial shedding. When the snails were treated with 1000 mg/kg PZQ, the cercarial production was re-established 15 days after treatment, but in lower numbers than those obtained before treatment, whereas the snails treated with 500 mg/kg OXA were able to shed cercariae in similar quantities to those observed before treatment. The association 250 mg/kg OXA+500 mg/kg PZQ, at the patent period, not only discontinued cercarial shedding, but also led to the "cure" of the snails, showing a synergistic effect of this combination of drugs. These results suggest that this model will be useful for selection of resistant parasites, as well as for screening new antischistosomal drugs.

Diversification of the insulin receptor family in the helminth parasite Schistosoma mansoni

Insulin signalling is a very ancient and well conserved pathway in metazoan cells, dependent on insulin receptors (IR) which are transmembrane proteins with tyrosine kinase activity. A unique IR is usually present in invertebrates whereas two IR members are found with different functions in vertebrates. This work demonstrates the existence of two distinct IR homologs (SmIR-1 and SmIR-2) in the parasite trematode Schistosoma mansoni. These two receptors display differences in several structural motifs essential for signalling and are differentially expressed in parasite tissues, suggesting that they could have distinct functions. The gene organization of SmIR-1 and SmIR-2 is similar to that of the human IR and to that of the IR homolog from Echinococcus multilocularis (EmIR), another parasitic platyhelminth. SmIR-1 and SmIR-2 were shown to interact with human pro-insulin but not with pro-insulin-like growth factor-1 in two-hybrid assays. Phylogenetic results indicated that SmIR-2 and EmIR might be functional orthologs whereas SmIR-1 would have emerged to fulfil specific functions in schistosomes.