Abstract
We showed previously that the Schistosoma japonicum insulin-like peptide (SjILP) binds the worm insulin receptors, thereby, activating the parasite’s insulin pathway and emphasizing its important role in regulating uptake of glucose, a nutrient essential for parasite survival. Here we show that SjILP is differentially expressed in the schistosome life cycle and is especially highly transcribed in eggs, miracidia, and adult female worms. RNA inference was employed to knockdown SjILP in adults in vitro, with suppression confirmed by significantly reduced protein production, declined adenosine diphosphate levels, and reduction in glucose consumption. Immunolocalization showed that SjILP is located to lateral gland cells of mature intra-ovular miracidia in the schistosome egg, and is distributed on the ciliated epithelium and internal cell masses of newly transformed miracidia. In schistosomula, SjILP is present on the tegument in two antero-lateral points, indicating highly polarized expression during cercarial transformation. Analysis of serum from S. japonicum-infected mice by ELISA using a recombinant form of SjILP as an antigen revealed IgG immunoreactivity to this molecule at 7 weeks post-infection indicating it is likely secreted from mature eggs into the host circulation. These findings provide further insights on ILP function in schistosomes and its essential roles in parasite survival and growth in different development stages.
Highlights
Schistosomiasis remains one of the most prevalent, insidious, and serious tropical parasitic diseases, with an estimated 200 million people infected in 76 countries [1,2]
A total of 43 genes involved in the insulin pathway have been identified to date for S. mansoni [7], S. haematobium [9], and S. japonicum [6], including those encoding Src homology-containing (SHC), Src homology 2-B proteins, phosphoinositide-3-kinase (PI3K), extracellular signal-regulated kinase (ERK), glycogen synthase (GYS), and glucose transport protein 4 (GTP4)
To determine whether the knockdown of Schistosoma japonicum insulin-like peptide (SjILP) Double Stranded RNA (dsRNA) was reflected at the protein level, we performed Western blot analysis using soluble antigen preparation (SWAP) of diced adults harvested on day 2 post-treatment with dsRNA and intact adult worms obtained on day 4 post-treatment with dsRNA
Summary
Schistosomiasis remains one of the most prevalent, insidious, and serious tropical parasitic diseases, with an estimated 200 million people infected in 76 countries [1,2]. Improved interventions for the control of schistosomiasis will rely on a better understanding of how schistosomes absorb host nutrients, neuro-endocrine hormones for their growth, development, and fecundity. Whereas there is much information regarding the mechanism of insulin signaling in Caenorhabditis elegans [5], it remains to be established whether the pathway and the regulation of glucose are similar in schistosomes. Genome-wide interrogation has revealed the presence of an insulin signaling pathway in Schistosoma japonicum [6], Schistosoma mansoni [7], and Schistosoma haematobium [8,9]. A total of 43 genes involved in the insulin pathway have been identified to date for S. mansoni [7], S. haematobium [9], and S. japonicum [6], including those encoding Src homology-containing (SHC), Src homology 2-B proteins, phosphoinositide-3-kinase (PI3K), extracellular signal-regulated kinase (ERK), glycogen synthase (GYS), and glucose transport protein 4 (GTP4)
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