Host insulin stimulates Echinococcus multilocularisinsulin signalling pathways and larval development

Abstract

BackgroundThe metacestode of the tapeworm Echinococcus multilocularis is the causative agent of alveolar echinococcosis, a lethal zoonosis. Infections are initiated through establishment of parasite larvae within the intermediate host’s liver, where high concentrations of insulin are present, followed by tumour-like growth of the metacestode in host organs. The molecular mechanisms determining the organ tropism of E. multilocularis or the influences of host hormones on parasite proliferation are poorly understood.ResultsUsing in vitro cultivation systems for parasite larvae we show that physiological concentrations (10 nM) of human insulin significantly stimulate the formation of metacestode larvae from parasite stem cells and promote asexual growth of the metacestode. Addition of human insulin to parasite larvae led to increased glucose uptake and enhanced phosphorylation of Echinococcus insulin signalling components, including an insulin receptor-like kinase, EmIR1, for which we demonstrate predominant expression in the parasite’s glycogen storage cells. We also characterized a second insulin receptor family member, EmIR2, and demonstrated interaction of its ligand binding domain with human insulin in the yeast two-hybrid system. Addition of an insulin receptor inhibitor resulted in metacestode killing, prevented metacestode development from parasite stem cells, and impaired the activation of insulin signalling pathways through host insulin.ConclusionsOur data indicate that host insulin acts as a stimulant for parasite development within the host liver and that E. multilocularis senses the host hormone through an evolutionarily conserved insulin signalling pathway. Hormonal host-parasite cross-communication, facilitated by the relatively close phylogenetic relationship between E. multilocularis and its mammalian hosts, thus appears to be important in the pathology of alveolar echinococcosis. This contributes to a closer understanding of organ tropism and parasite persistence in larval cestode infections. Furthermore, our data show that Echinococcus insulin signalling pathways are promising targets for the development of novel drugs.

Recent advances in Echinococcus genomics and stem cell research

“…Surely of high relevance for host-parasite interaction mechanisms is also the presence of evolutionarily conserved signalling systems in Echinococcus, such as components of the epidermal growth factor (EGF)-, fibroblast growth factor (FGF)-, transforming growth factor-␤ (TGF-␤)-, and Insulin-signal transduction cascades (Brehm, 2010b;Tsai et al, 2013;Zheng et al, 2013). Host insulin has, for example, recently been demonstrated to stimulate E. multilocularis developmental processes via interaction with parasite surface receptors of the Insulin-Receptor family (Hemer et al, 2014), and host-derived EGF is known to induce the Echinococcus mitogen activated protein kinase (MAPK) cascade, probably through direct interaction with parasite EGF-receptors (Spiliotis et al, 2006).…”

“…These germinative cells were the only cells that underwent proliferation during regeneration. Thus, E. multilocularis primary cell preparations are an ideal system for the functional study of genes and pathways in germinative cells, particularly if used in combination with specific pharmacological inhibitors or with RNA interference methods for gene-specific knockdown (Hemer et al, 2014;Spiliotis et al, 2010). Furthermore, they have been proposed to be an in vitro experimental model for the developmental processes that occur during the metamorphosis from oncosphere to metacestode, and during metastasis (Olson et al, 2012).…”

“…Previous studies clearly showed that some of these receptors were able to interact with human ligands, including the interaction in vitro of the E. multilocularis insulin receptors EmIR1 and EmIR2 with human insulin (Hemer et al, 2014;Konrad et al, 2003). Recently, it was shown that physiologically relevant concentrations of insulin added to in vitro culture are indeed able to activate the E. multilocularis receptors and to promote growth and cell proliferation in metacestode vesicles, as well as the proliferation and regeneration of new vesicles in primary cells (Hemer et al, 2014). Altogether, these results strongly support the hypothesis that the parasite is able to detect host insulin by means of conserved signalling mechanisms.…”

“…Furthermore, due to their importance in malignant transformation, the biochemistry of kinases is exceptionally well studied and research has already brought up a plethora of inhibitory compounds, many of which are currently in use to treat various forms of cancer (Brehm, 2014). Several prominent kinase inhibitors such as Imatinib, directed against Abl-kinases, BI 2536 (Polo-like kinase) or pyridinylimidazoles (p38 MAPK) have already been shown to exert anti-Echinococcus activities in vitro by inhibition of the orthologous parasite factors (Gelmedin et al, 2008;Hemer et al, 2014;Schubert et al, 2014) and are thus promising lead compounds for the design of related small molecule compounds that show a high specificity for parasite kinases (Brehm, 2014). Interestingly, genomic and transcriptomic analyses also revealed why some drugs are not effective against larval cestodes.…”

Biology and Systematics of Echinococcus

“…Following evagination, protoscoleces are initially very active as they have to rapidly locate and attach to the mucosal surface in the crypts of Lieberkuhn to avoid being swept out of the small intestine, with some actually within the crypts by 6 h after infection (Thompson, 1977). As such, motility is enhanced by a well-developed nervous system and glycogen energy reserves (Brownlee et al, 1994;Camicia et al, 2013;Hemer et al, 2014;Smyth, 1967). The evaginated protoscoleces are rich in glycogen which acts as an energy reserve although this is rapidly used up, usually within 3 h (Smyth, 1967).…”