Structure and Bioactivity of Neuropeptide F from the Human Parasites Schistosoma mansoni and Schistosoma japonicum

Abstract

The blood flukes Schistosoma mansoni and Schistosoma japonicum inflict immense suffering as agents of human schistosomiasis. Previous investigations have found the nervous systems of these worms contain abundant immunoreactivity to antisera targeting invertebrate neuropeptide Fs (NPFs) as well as structurally similar neuropeptides of the mammalian neuropeptide Y (NPY) family. Here, cDNAs encoding NPF in these worms were identified, and the mature neuropeptides from the two species differed by only a single amino acid. Both neuropeptides feature the characteristics common among NPFs; they are 36 amino acids long with a carboxyl-terminal Gly-Arg-X-Arg-Phe-amide and Tyr residues at positions 10 and 17 from the carboxyl terminus. Synthetic S. mansoni NPF potently inhibits the forskolin-stimulated accumulation of cAMP in worm homogenates, with significant effects at 10 ؊11 M. This is the first demonstration of an endogenous inhibition of cAMP by an NPF, and because this is the predominant pathway associated with vertebrate NPY family peptides, it demonstrates a conservation of downstream signaling pathways used by NPFs and NPY peptides.Blood fluke parasites of the genus Schistosoma are the most important metazoan parasites of humans and are the etiological agents of schistosomiasis (bilharzia), which afflicts over 200 million people. Schistosomiasis ranks second, behind only malaria, in terms of its overall negative socio-economic and public health impact on the tropical and subtropical world, and it remains among the top five disease priorities of the World Health Organization (WHO) 1 (1). Control of the disease rests almost solely on chemotherapy using the anthelmintic praziquantel (2-4). Most disturbingly, the long term utility of praziquantel has been brought into question because of growing reports of infections not responding to the recommended dosage (5-8) and worms with decreased sensitivity (9, 10). WHO has accordingly identified research into the basic biology of schistosomes as a priority, with the hope of identifying targets for the next generation of antischistosomal drugs (1).Schistosomes belong to the class Trematoda of the phylum Platyhelminthes (flatworms) and, as such, are among the simplest extant animals to display brain development with the concomitant distinction between central and peripheral neuronal elements. One distinct feature of platyhelminths and other early diverging phyla is a prominent peptidergic component within their nervous systems. One family of neuropeptides abundant among these early animals is the neuropeptide F (NPF) family (11-14). NPFs are 36 -40-amino acid peptides featuring a carboxyl-terminal Gly-Arg-X-Arg-Phe-amide (GRXRF-NH 2 ) motif and tyrosine residues at positions 10 and 17 relative to the carboxyl terminus.These characteristics are common to those of vertebrate NPY family peptides, 36 amino acid neuropeptides with RXR(F/Y)-NH 2 carboxyl termini, Tyr residues at positions 10 and 17 relative to the carboxyl termini, and prolines in a PXXPXXP motif near the amino ter...

Neuropeptide signalling systems in flatworms

“…A more compelling case for linking invertebrate NPF receptors to the inhibition of cAMP comes from schistosomes. Schistosome NPF inhibits the accumulation of cAMP in schistosome homogenates at a threshold of 10 x11 M (Humphries et al 2004). The inhibition is quite specific, with the most potent action reserved only for the endogenous schistosome peptide, but could also be reproduced less potently by mxNPF and porcine NPY.…”

“…Furthermore, there was chromatographic evidence that the parasite antigens were structurally similar to the 36 amino acid peptide common to NPY family members. Chromatographic analysis of peptide extracts from D. merlangi (Maule et al 1989 a), M. expansa (Maule et al 1991) and S. mansoni (Humphries et al 2004) found a single peak of PP immunoreactivity which co-eluted with other NPY family members from columns which separate on the basis of size and hydrophobicity. This type of evidence led to the hypothesis that there was an NPY-like neuropeptide present in flatworms even before the identification of a specific peptide from the phylum.…”

“…References : A. triangulatus (Dougan et al 2002). S. mansoni and S. japonicum (Humphries et al 2004). M. expansa .…”

“…In contrast, at least some of the neuropeptides present in parasitic flatworms have restricted roles in their mammalian hosts. Also, the endogenous neuropeptides are remarkably potent in parasitic worms ; in schistosomes, some peptides have threshold activities in the low nanomolar or high picomolar range Humphries et al 2004). This paper will provide an overview of what is known about the role of neuropeptides in platyhelminths, keeping an eye on the consideration that molecules involved in the neuropeptidergic signalling could be attractive targets for novel drugs to treat infections with platyhelminths.…”

Identification, tissue distribution and orexigenic activity of neuropeptide F (NPF) in penaeid shrimp

“…Since the initial description (Maule et al, 1991), additional isoforms of NPF have been identified from members of many taxa, including the Rotifera, Platyhelminthes, Mollusca, Annelida and Arthropoda (e.g. Rajapara et al, 1992;Brown et al, 1999;Dougan et al, 2002;Stanek et al, 2002;Humphries et al, 2004;Roller et al, 2008;Nuss et al, 2010).…”