Ceramide synthase 2 knockdown suppresses trophozoite growth, migration, in vitro encystment and excystment of Entamoeba invadens

Ancestral TALE homeobox protein transcription factor regulates actin dynamics and cellular activities of protozoan parasite Entamoeba invadens

Entamoeba histolytica causes invasive amoebiasis, an important neglected tropical disease with a significant global health impact. The pathogenicity and survival of E. histolytica and its reptilian equivalent, Entamoeba invadens, relies on its ability to exhibit efficient motility, evade host immune responses, and exploit host resources, all of which are governed by the actin cytoskeleton remodeling. Our study demonstrates the early origin and the regulatory role of TALE homeobox protein EiHbox1 in actin-related cellular processes. Several genes involved in different biological pathways, including actin dynamics are differentially expressed in EiHbox1 silenced cells. EiHbox1 silenced parasites showed disrupted F-actin organization and loss of cellular polarity. EiHbox1's presence in the anterior region of migrating cells further suggests its involvement in maintaining cellular polarity. Loss of polarized morphology of EiHbox1 silenced parasites leads to altered motility from fast, directionally persistent, and highly chemotactic to slow, random, and less chemotactic, which subsequently leads to defective aggregation during encystation. EiHbox1 knockdown also resulted in a significant reduction in phagocytic capacity and poor capping response. These findings highlight the importance of EiHbox1 of E. invadens in governing cellular processes crucial for their survival, pathogenicity, and evasion of the host immune system.

Stage-Specific De Novo Synthesis of Very-Long-Chain Dihydroceramides Confers Dormancy to Entamoeba Parasites

Amoebiasis is a parasitic disease caused by Entamoeba histolytica infection and is a serious public health problem worldwide due to ill-prepared preventive measures as well as its high morbidity and mortality rates. Amoebiasis transmission is solely mediated by cysts. Cysts are produced by the differentiation of proliferative trophozoites in a process termed "encystation." Entamoeba encystation is a fundamental cell differentiation process and proceeds with substantial changes in cell metabolites, components, and morphology, which occur sequentially in an orchestrated manner. Lipids are plausibly among these metabolites that function as key factors for encystation. However, a comprehensive lipid analysis has not been reported, and the involved lipid metabolic pathways remain largely unknown. Here, we exploited the state-of-the-art untargeted lipidomics and characterized 339 molecules of 17 lipid subclasses. Of these, dihydroceramide (Cer-NDS) was found to be among the most induced lipid species during encystation. Notably, in encysting cells, amounts of Cer-NDS containing very long N-acyl chains (≥26 carbon) were more than 30-fold induced as the terminal product of a de novo metabolic pathway. We also identified three ceramide synthase genes responsible for producing the very-long-chain Cer-NDS molecules. These genes were upregulated during encystation. Furthermore, these ceramide species were shown to be indispensable for generating membrane impermeability, a prerequisite for becoming dormant cyst that shows resistance to environmental assault inside and outside the host for transmission. Hence, the lipid subclass of Cer-NDS plays a crucial role for Entamoeba cell differentiation and morphogenesis by alternating the membrane properties.IMPORTANCE Entamoeba is a protozoan parasite that thrives in its niche by alternating its two forms between a proliferative trophozoite and dormant cyst. Cysts are the only form able to transmit to a new host and are differentiated from trophozoites in a process termed "encystation." During Entamoeba encystation, cell metabolites, components, and morphology drastically change, which occur sequentially in an orchestrated manner. Lipids are plausibly among these metabolites. However, the involved lipid species and their metabolic pathways remain largely unknown. Here, we identified dihydroceramides (Cer-NDSs) containing very long N-acyl chains (C₂₆ to C₃₀) as a key metabolite for Entamoeba encystation by our state-of-the-art untargeted lipidomics. We also showed that these Cer-NDSs are critical to generate the membrane impermeability, a prerequisite for this parasite to show dormancy as a cyst that repels substances and prevents water loss. Hence, ceramide metabolism is essential for Entamoeba to maintain the parasitic lifestyle.

Signals and signal transduction pathways in Entamoeba histolytica during the life cycle and when interacting with bacteria or human cells

Entamoeba histolytica is the etiological agent of amebiasis in humans. This ameba parasite resides as a commensal in the intestine where it shares intestinal resources with the bacterial microbiome. In the intestinal ecosystem, the ameba encysts and eventually develops disease by invading the tissues. E. histolytica possesses cell surface receptors for the proper sensing of signals involved in encystation or sustaining parasite interaction with bacteria and human cells. Among those receptors are the Gal/GalNAc lectin, G protein-coupled receptors, and transmembrane kinases. In addition there are recently discovered, promising proteins, including orthologs of Toll-type receptors and β trefoil lectins. These proteins trigger a wide variety of signal transduction pathways; however, most of the players involved in the signaling pathways evoked in this parasite are unknown. This review provides an overview of amoebic receptors and their role in encystation, adherence to bacteria or human cells, as well as the reported intracellular signal transduction processes that they can trigger. This knowledge is essential for understanding the lifestyle of E. histolytica and its cytopathic effect on bacteria and human cells that are responsible for infection.

Entamoeba stage conversion: progress and new insights

Entamoeba histolytica, an anaerobic protozoan, is an important global health problem. This parasite has a biphasic life cycle consisting of a dormant cyst stage which is environmentally resistant and transmits the infection, and the proliferative trophozoite stage which is motile and causes invasive disease. The stage conversion process remains poorly understood despite being central to amoebic biology. In this review, we will highlight recent progress in our understanding of Entamoeba stage conversion including dissecting transcriptome analysis in development, characterization of transcriptional networks, demonstration of epigenetic regulation, and role of small molecules that regulate Entamoeba development.