Entamoeba histolytica: lipid rafts are involved in adhesion of trophozoites to host extracellular matrix components

Molecular interplays of the Entamoeba histolytica endosomal sorting complexes required for transport during phagocytosis

Entamoeba histolytica, the causative agent of human amoebiasis, exhibits a continuous membrane remodelling to exert its virulence properties. During this dynamic process, the Endosomal Sorting Complexes Required for Transport (ESCRT) machinery is a key player, particularly in phagocytosis, a virulence hallmark of this parasite. In addition to ESCRT, other molecules contribute to membrane remodelling, including the EhADH adhesin, EhRabs, actin, and the lysobisphosphatidic acid (LBPA). The endocytosis of a prey or molecules induces membrane invaginations, resulting in endosome and multivesicular bodies (MVBs) formation for cargo delivery into lysosomes. Alternatively, some proteins are recycled or secreted. Most of these pathways have been broadly characterized in other biological systems, but poorly described in protozoan parasites. Here, we encompass 10 years of ESCRT research in E. histolytica, highlighting the role of the ESCRT-I and ESCRT-III components and the EhADH and EhVps4-ATPase accessory proteins during phagocytosis. In particular, EhADH exhibits a multifunctional role along the endocytic pathway, from cargo recognition to endosome maturation and lysosomal degradation. Interestingly, the interaction of EhADH with EhVps32 seems to shape a concurrent route to the conventional one for MVBs biogenesis, that could optimize their formation. Furthermore, this adhesin is secreted, but its role in this event remains under study. Other components from the endosomal pathway, such as EhVps23 and LBPA, are also secreted. A proteomic approach performed here, using an anti-LBPA antibody, revealed that some proteins related to membrane trafficking, cellular transport, cytoskeleton dynamics, and transcriptional and translational functions are secreted and associated to LBPA. Altogether, the accumulated knowledge around the ESCRT machinery in E. histolytica, points it out as a dynamic platform facilitating the interaction of molecules participating in different cellular events. Seen as an integrated system, ESCRTs lead to a better understanding of E. histolytica phagocytosis.

Asymptomatic Intestinal Parasitic Infestations among Children Under Five Years in Selected Communities in the Ho Municipality, Ghana

Background

The study investigated intestinal parasitic infestations (IPIs) and possible risk factors associated with asymptomatic children under five (5) years in five (5) selected communities in the Ho Municipality.

Methods

The study design was cross- sectional, with a simple random sampling technique involving 150 asymptomatic children under 5 years from 5 selected communities (Klave, Hoe, Freetown, Dave and Godokpe) in the Ho Municipality. A questionnaire was used to obtain socio-demographics and other relevant parameters. Direct wet preparation, formol-ether concentration and Modified ZN staining techniques were used for the identification of intestinal parasites from participants' stool samples. The Fisher's exact test and binary logistic regression analysis were used to determine the difference in IPIs proportions and assess the risk factors associated with IPIs respectively.

Results

The overall IPIs cases was 14% (21/150). Cryptosporidium spp was most predominant [5.3% (8/150)], followed by Entamoeba spp [3.3% (5/150)], Cyclospora cayetenensis [2.7% (4/150)], Ascaris lumbricoides [1.3% (2/150)], Giardia lamblia [0.7% (1/150)] and Strongyloides stercoralis [0.7% (1/150)]. Children in rural communities (23.4%) recorded significantly higher case rate compared to those in urban communities (9.8%0), (p=0.04). Lower educational attainment of mother [OR=0.55, 95% CI (0.37 – 0.83), p-value = 0.015] and residence in rural communities [OR = 0.53, 95% CI (0.33–0.88)], p-value = 0.025] were significantly associated with IPIs.

Conclusion

Asymptomatic IPIs are quite prevalent among children under 5 years in the Ho Municipality. The study thus recommends active sensitization programs for parents/guardians on preventive measures and school health programs should be instituted in rural communities.

Low molecular weight protein tyrosine phosphatase (LMW-PTP2) protein can potentially modulate virulence of the parasite Entamoeba histolytica

The Entamoeba histolytica parasite is the causative agent of amebiasis, infecting approximately 1% of the world population and causing 100,000 deaths per year. It binds to Fibronectin (FN), activating signaling pathways regulated by kinases and phosphatases. EhLMW-PTPs genes from E. histolytica encode for Low Molecular Weight Tyrosine Phosphatases expressed in trophozoites and amoebic cysts. The role of these phosphatases in the virulence of the parasite has not yet been well characterized. Our results showed a differential expression of the EhLMW-PTPs, at the mRNA and protein levels, in an asynchronous trophozoites culture. Furthermore, we observed that trophozoites transfected that overexpressed EhLMW-PTP2 phagocytized fewer erythrocytes, possibly due to decreased phagocytic cups, and showed deficiencies in adherence to FN and less cytopathic effect. These analyzes suggest that the parasite's EhLMW-PTPs have an essential role in the mechanisms of proliferation, adhesion, and phagocytosis, regulating its pathogenicity.

Lipids in Entamoeba histolytica: Host-Dependence and Virulence Factors

Lipids are essential players in parasites pathogenesis. In particular, the highly phagocytic trophozoites of Entamoeba histolytica, the causative agent of amoebiasis, exhibit a dynamic membrane fusion and fission, in which lipids strongly participate; particularly during the overstated motility of the parasite to reach and attack the epithelia and ingest target cells. Synthesis and metabolism of lipids in this protozoan present remarkable difference with those performed by other eukaryotes. Here, we reviewed the current knowledge on lipids in E. histolytica. Trophozoites synthesize phosphatidylcholine and phosphatidylethanolamine by the Kennedy pathway; and sphingolipids, phosphatidylserine, and phosphatidylinositol, by processes similar to those used by other eukaryotes. However, trophozoites lack enzymes for cholesterol and fatty acids synthesis, which are scavenged from the host or culture medium by specific mechanisms. Cholesterol, a fundamental molecule for the expression of virulence, is transported from the medium into the trophozoites by EhNPC1 and EhNPC2 proteins. Inside cells, lipids are distributed by different pathways, including by the participation of the endosomal sorting complex required for transport (ESCRT), involved in vesicle fusion and fission. Cholesterol interacts with the phospholipid lysobisphosphatidic acid (LBPA) and EhADH, an ALIX family protein, also involved in phagocytosis. In this review, we summarize the known information on phospholipids synthesis and cholesterol transport as well as their metabolic pathways in E. histolytica; highlighting the mechanisms used by trophozoites to dispose lipids involved in the virulence processes.

Reduced expression of a rhomboid protease, EhROM1, correlates with changes in the submembrane distribution and size of the Gal/GalNAc lectin subunits in the human protozoan parasite, Entamoeba histolytica

Entamoeba histolytica is a food- and waterborne parasite that causes amebic dysentery and amoebic liver abscesses. Adhesion is one of the most important virulence functions as it facilitates motility, colonization of host, destruction of host tissue, and uptake of nutrients by the parasite. The parasite cell surface adhesin, the Gal/GalNAc lectin, facilitates parasite-host interaction by binding to galactose or N-acetylgalactosamine residues on host components. It is composed of heavy (Hgl), intermediate (Igl), and light (Lgl) subunits. Igl is constitutively localized to lipid rafts (cholesterol-rich membrane domains), whereas Hgl and Lgl transiently associate with rafts. When all three subunits are localized to rafts, galactose-sensitive adhesion is enhanced. Thus, submembrane location may regulate the function of this adhesion. Rhomboid proteases are a conserved family of intramembrane proteases that also participate in the regulation of parasite-host interactions. In E. histolytica, one rhomboid protease, EhROM1, cleaves Hgl as a substrate, and knockdown of its expression inhibits parasite-host interactions. Since rhomboid proteases are found within membranes, it is not surprising that lipid composition regulates their activity and enzyme-substrate binding. Given the importance of the lipid environment for both rhomboid proteases and the Gal/GalNAc lectin, we sought to gain insight into the relationship between rhomboid proteases and submembrane location of the lectin in E. histolytica. We demonstrated that EhROM1, itself, is enriched in highly buoyant triton-insoluble membranes reminiscent of rafts. Reducing rhomboid protease activity, either pharmacologically or genetically, correlated with an enrichment of Hgl and Lgl in rafts. In a mutant cell line with reduced EhROM1 expression, there was also a significant augmentation of the level of all three Gal/GalNAc subunits on the cell surface and an increase in the molecular weight of Hgl and Lgl. Overall, the study provides insight into the molecular mechanisms governing parasite-host adhesion for this pathogen.

Host Invasion by Pathogenic Amoebae: Epithelial Disruption by Parasite Proteins

The epithelium represents the first and most extensive line of defence against pathogens, toxins and pollutant agents in humans. In general, pathogens have developed strategies to overcome this barrier and use it as an entrance to the organism. Entamoeba histolytica, Naegleriafowleri and Acanthamoeba spp. are amoebae mainly responsible for intestinal dysentery, meningoencephalitis and keratitis, respectively. These amoebae cause significant morbidity and mortality rates. Thus, the identification, characterization and validation of molecules participating in host-parasite interactions can provide attractive targets to timely intervene disease progress. In this work, we present a compendium of the parasite adhesins, lectins, proteases, hydrolases, kinases, and others, that participate in key pathogenic events. Special focus is made for the analysis of assorted molecules and mechanisms involved in the interaction of the parasites with epithelial surface receptors, changes in epithelial junctional markers, implications on the barrier function, among others. This review allows the assessment of initial host-pathogen interaction, to correlate it to the potential of parasite invasion.

Contribution of neutral sphingomyelinases to in vitro virulence of Entamoeba histolytica

Amoebiasis is a worldwide health problem caused by the pathogen Entamoeba histolytica. Several virulence factors have been implicated in host invasion, immune evasion, and tissue damage. There are still new factors that remain to be elucidated and characterized. In this work, we obtained amoebic transfectants overexpressing three of the neutral sphingomyelinase enzymes encoded in the E. histolytica genome. The EhnSM3 overexpression induced an increase in hemolytic and cytotoxic activities, besides an increase in gene expression of amoebapore A, B, and C. Meanwhile the EhnSM1 and EhnSM2 overexpression caused an increase in cytopathic activity. In all the neutral sphingomyelinases overexpressing strains, the gene expression levels for cysteine proteinase 5, adhesin 112 and, heavy and light Gal/GalNAc lectin subunits were not affected. We propose that the increase of cytotoxic and lytic effect of EhnSM3 overexpressed strain can be related to the sum of the effect of EhnSM3 plus amoebapores, in a process cell contact-dependent or as mediator by inducing the gene expression of amoebapores enabling a link between EhnSM3 with the virulence phenotype in E. histolytica. Our results suggest a differential role for neutral sphingomyelinases in E. histolytica virulence.

Non-vesicular Lipid Transport Machinery in Entamoeba histolytica

Eukaryotic cells are organized into separate membrane-bound compartments that have specialized biochemical signature and function. Maintenance and regulation of distinct identity of each compartment is governed by the uneven distribution and intra-cellular movement of two essential biomolecules, lipids, and proteins. Non-vesicular lipid transport mediated by lipid transfer proteins plays a pivotal role in intra-cellular lipid trafficking and homeostasis whereas vesicular transport plays a central role in protein trafficking. Comparative study of lipid transport machinery in protist helps to better understand the pathogenesis and parasitism, and provides insight into eukaryotic evolution. Amebiasis, which is caused by Entamoeba histolytica, is one of the major enteric infections in humans, resulting in 40–100 thousand deaths annually. This protist has undergone remarkable alterations in the content and function of its sub-cellular compartments as well represented by its unique diversification of mitochondrion-related organelle, mitosome. We conducted domain-based search on AmoebaDB coupled with bioinformatics analyses and identified 22 potential lipid transfer protein homologs in E. histolytica, which are grouped into several sub-classes. Such in silico analyses have demonstrated the existence of well-organized lipid transport machinery in this parasite. We summarized and discussed the conservation and unique features of the whole repertoire of lipid transport proteins in E. histolytica.

Entamoeba histolytica: Host parasite interactions at the colonic epithelium

Entamoeba histolytica (Eh) is the protozoan parasite responsible for intestinal amebiasis and interacts dynamically with the host intestinal epithelium during disease pathogenesis. A multifaceted pathogenesis profile accounts for why 90% of individuals infected with Eh are largely asymptomatic. For 100 millions individuals that are infected each year, key interactions within the intestinal mucosa dictate disease susceptibility. The ability for Eh to induce amebic colitis and disseminate into extraintestinal organs depends on the parasite competing with indigenous bacteria and overcoming the mucus barrier, binding to host cells inducing their cell death, invasion through the mucosa and outsmarting the immune system. In this review we summarize how Eh interacts with the intestinal epithelium and subverts host defense mechanisms in disease pathogenesis.

EhNPC1 and EhNPC2 Proteins Participate in Trafficking of Exogenous Cholesterol in Entamoeba histolytica Trophozoites: Relevance for Phagocytosis

Entamoeba histolytica, the highly phagocytic protozoan causative of human amoebiasis lacks the machinery to synthesize cholesterol. Here, we investigated the presence of NPC1 and NPC2 proteins in this parasite, which are involved in cholesterol trafficking in mammals. Bioinformatics analysis revealed one Ehnpc1 and two Ehnpc2 genes. EhNPC1 appeared as a transmembrane protein and both EhNPC2 as peripheral membrane proteins. Molecular docking predicted that EhNPC1 and EhNPC2 bind cholesterol and interact with each other. Genes and proteins were identified in trophozoites. Serum pulse-chase and confocal microscopy assays unveiled that after trophozoites sensed the cholesterol source, EhNPC1 and EhNPC2 were organized around the plasma membrane in a punctuated pattern. Vesicles emerged and increased in number and size and some appeared full of cholesterol with EhNPC1 or EhNPC2 facing the extracellular space. Both proteins, but mostly EhNPC2, were found out of the cell associated with cholesterol. EhNPC1 and cholesterol formed networks from the plasma membrane to the nucleus. EhNPC2 appeared in erythrocytes that were being ingested by trophozoites, co-localizing with cholesterol of erythrocytes, whereas EhNPC1 surrounded the phagocytic cup. EhNPC1 and EhNPC2 co-localized with EhSERCA in the endoplasmic reticulum and with lysobisphosphatidic acid and EhADH (an Alix protein) in phagolysosomes. Immunoprecipitation assays confirmed the EhNPC1 and EhNPC2 association with cholesterol, EhRab7A and EhADH. Serum starved and blockage of cholesterol trafficking caused a low rate of phagocytosis and incapability of trophozoites to produce damage in the mouse colon. Ehnpc1 and Ehnpc2 knockdown provoked in trophozoites a lower intracellular cholesterol concentration and a diminished rate of phagocytosis; and Ehnpc1 silencing also produced a decrease of trophozoites movement. Trafficking of EhNPC1 and EhNPC2 during cholesterol uptake and phagocytosis as well as their association with molecules involved in endocytosis strongly suggest that these proteins play a key role in cholesterol uptake.

NPC1 and NPC2 proteins are involved in cholesterol trafficking in mammals. Using different approaches, we have detected the orthologues EhNPC1 and EhNPC2 proteins in Entamoeba histolytica. Trophozoites are particularly rich in membranes and vacuoles, but they do not possess the machinery to synthetize cholesterol. Thus, they are completely dependent on molecules able to “fish” cholesterol from the medium. The relevance of our findings lies in the fact that cholesterol is fundamental for endocytosis and motility; and, phagocytosis is an important nutritional and virulence factor for E. histolytica. In silico and experimental strategies, using U18666A to arrest cholesterol trafficking, as well as, knockdown mutants, showed that EhNPC1 and EhNPC2 participate in cholesterol uptake and trafficking in this parasite. They are secreted by trophozoites and directly involved in erythrophagocytosis and motility. Our findings revealed E. histolytica as one of the first protozoa in which these proteins are being characterized. Moreover, E. histolytica provides an excellent and less complicated model to elucidate the intricate event of cholesterol trafficking in eukaryotic cells. The relevance of cholesterol transport for the parasite virulence and the involvement of EhNPC1 and EhNPC2 in this process, make these proteins promising targets for therapy strategies development against the parasite.

RNA-seq analysis of early enteromyxosis in turbot (Scophthalmus maximus): new insights into parasite invasion and immune evasion strategies

Enteromyxum scophthalmi, an intestinal myxozoan parasite, is the causative agent of a threatening disease for turbot (Scophthalmus maximus, L.) aquaculture. The colonisation of the digestive tract by this parasite leads to a cachectic syndrome associated with high morbidity and mortality rates. This myxosporidiosis has a long pre-patent period and the first detectable clinical and histopathological changes are subtle. The pathogenic mechanisms acting in the early stages of infection are still far from being fully understood. Further information on the host-parasite interaction is needed to assist in finding efficient preventive and therapeutic measures. Here, a RNA-seq-based transcriptome analysis of head kidney, spleen and pyloric caeca from experimentally-infected and control turbot was performed. Only infected fish with early signs of infection, determined by histopathology and immunohistochemical detection of E. scophthalmi, were selected. The RNA-seq analysis revealed, as expected, less intense transcriptomic changes than those previously found during later stages of the disease. Several genes involved in IFN-related pathways were up-regulated in the three organs, suggesting that the IFN-mediated immune response plays a main role in this phase of the disease. Interestingly, an opposite expression pattern had been found in a previous study on severely infected turbot. In addition, possible strategies for immune system evasion were suggested by the down-regulation of different genes encoding complement components and acute phase proteins. At the site of infection (pyloric caeca), modulation of genes related to different structural proteins was detected and the expression profile indicated the inhibition of cell proliferation and differentiation. These transcriptomic changes provide indications regarding the mechanisms of parasite attachment to and invasion of the host. The current results contribute to a better knowledge of the events that characterise the early stages of turbot enteromyxosis and provide valuable information to identify molecular markers for early detection and control of this important parasitosis.

Analysis of cytochrome b(5) reductase-mediated metabolism in the phytopathogenic fungus Zymoseptoria tritici reveals novel functionalities implicated in virulence

Septoria tritici blotch (STB) caused by the Ascomycete fungus Zymoseptoria tritici is one of the most economically damaging diseases of wheat worldwide. Z. tritici is currently a major target for agricultural fungicides, especially in temperate regions where it is most prevalent. Many fungicides target electron transfer enzymes because these are often important for cell function. Therefore characterisation of genes encoding such enzymes may be important for the development of novel disease intervention strategies. Microsomal cytochrome b5 reductases (CBRs) are an important family of electron transfer proteins which in eukaryotes are involved in the biosynthesis of fatty acids and complex lipids including sphingolipids and sterols. Unlike the model yeast Saccharomyces cerevisiae which possesses only one microsomal CBR, the fully sequenced genome of Z. tritici bears three possible microsomal CBRs. RNA sequencing analysis revealed that ZtCBR1 is the most highly expressed of these genes under all in vitro and in planta conditions tested, therefore ΔZtCBR1 mutant strains were generated through targeted gene disruption. These strains exhibited delayed disease symptoms on wheat leaves and severely limited asexual sporulation. ΔZtCBR1 strains also exhibited aberrant spore morphology and hyphal growth in vitro. These defects coincided with alterations in fatty acid, sphingolipid and sterol biosynthesis observed through GC-MS and HPLC analyses. Data is presented which suggests that Z. tritici may use ZtCBR1 as an additional electron donor for key steps in ergosterol biosynthesis, one of which is targeted by azole fungicides. Our study reports the first functional characterisation of CBR gene family members in a plant pathogenic filamentous fungus. This also represents the first direct observation of CBR functional ablation impacting upon fungal sterol biosynthesis.

Small GTPase Rab21 mediates fibronectin induced actin reorganization in Entamoeba histolytica: implications in pathogen invasion

The protozoan parasite Entamoeba histolytica causes a wide spectrum of intestinal infections. In severe cases, the trophozoites can breach the mucosal barrier, invade the intestinal epithelium and travel via the portal circulation to the liver, where they cause hepatic abscesses, which can prove fatal if left untreated. The host Extra Cellular Matrix (ECM) plays a crucial role in amoebic invasion by triggering an array of cellular responses in the parasite, including induction of actin rich adhesion structures. Similar actin rich protrusive structures, known as 'invadosomes', promote chemotactic migration of the metastatic cancer cells and non-transformed cells by remodeling the ECM. Recent studies showed a central role for Rab GTPases, the master regulators of vesicular trafficking, in biogenesis of invadosomes. Here, we showed that fibronectin, a major host ECM component induced actin remodeling in the parasite in a Rab21 dependent manner. The focalized actin structures formed were reminiscent of the mammalian invadosomes. By using various approaches, such as immunofluorescence confocal microscopy and scanning electron microscopy, along with in vitro invasion assay and matrix degradation assay, we show that the fibronectin induced formation of amoebic actin dots depend on the nucleotide status of the GTPase. The ECM components, fibronectin and collagen type I, displayed differential control over the formation of actin dots, with fibronectin positively and collagen type I negatively modulating it. The cell surface adhesion molecule Gal/GalNAc complex was also found to impose additional regulation on this process, which might have implication in collagen type I mediated suppression of actin dots.

The role of carbohydrates in infection strategies of enteric pathogens

Enteric pathogens cause considerable public health concerns worldwide including tropical regions. Here, we review the roles of carbohydrates in the infection strategies of various enteric pathogens including viruses, bacteria and protozoa, which infect the epithelial lining of the human and animal intestine. At host cell entry, enteric viruses, including norovirus, recognize mainly histo-blood group antigens. At the initial step of bacterial infections, carbohydrates also function as receptors for attachment. Here, we describe the function of carbohydrates in infection by Salmonella enterica and several bacterial species that produce a variety of fimbrial adhesions. During invasion by enteropathogenic protozoa, apicomplexan parasites utilize sialic acids or sulfated glycans. Carbohydrates serve as receptors for infection by these microbes; however, their usage of carbohydrates varies depending on the microbe. On the surface of the mucosal tissues of the gastrointestinal tract, various carbohydrate moieties are present and play a crucial role in infection, representing the site of infection or route of access for most microbes. During the infection and/or invasion process of the microbes, carbohydrates function as receptors for various microbes, but they can also function as a barrier to infection. One approach to develop effective prophylactic and therapeutic antimicrobial agents is to modify the drug structure. Another approach is to modify the mode of inhibition of infection depending on the individual pathogen by using and mimicking the interactions with carbohydrates. In addition, similarities in mode of infection may also be utilized. Our findings will be useful in the development of new drugs for the treatment of enteric pathogens.

Interaction of pathogens with host cholesterol metabolism

PURPOSE OF REVIEW

Pathogens of different taxa, from prions to protozoa, target cellular cholesterol metabolism to advance their own development and to impair host immune responses, but also causing metabolic complications, for example, atherosclerosis. This review describes recent findings of how pathogens do it.

RECENT FINDINGS

A common theme in interaction between pathogens and host cholesterol metabolism is pathogens targeting lipid rafts of the host plasma membrane. Many intracellular pathogens use rafts as an entry gate, taking advantage of the endocytic machinery and high abundance of outward-looking molecules that can be used as receptors. At the same time, disruption of the rafts' functional capacity, achieved by the pathogens through a number of various means, impairs the ability of the host to generate immune response, thus helping pathogen to thrive. Pathogens cannot synthesize cholesterol, and salvaging host cholesterol helps pathogens build advanced cholesterol-containing membranes and assembly platforms. Impact on cholesterol metabolism is not limited to the infected cells; proteins and microRNAs secreted by infected cells affect lipid metabolism systemically.

SUMMARY

Given an essential role that host cholesterol metabolism plays in pathogen development, targeting this interaction may be a viable strategy to fight infections, as well as metabolic complications of the infections.

Amoebic PI3K and PKC is required for Jurkat T cell death induced by Entamoeba histolytica

The enteric protozoan parasite Entamoeba histolytica is the causative agent of human amebiasis. During infection, adherence of E. histolytica through Gal/GalNAc lectin on the surface of the amoeba can induce caspase-3-dependent or -independent host cell death. Phosphorylinositol 3-kinase (PI3K) and protein kinase C (PKC) in E. histolytica play an important function in the adhesion, killing, or phagocytosis of target cells. In this study, we examined the role of amoebic PI3K and PKC in amoeba-induced apoptotic cell death in Jurkat T cells. When Jurkat T cells were incubated with E. histolytica trophozoites, phosphatidylserine (PS) externalization and DNA fragmentation in Jurkat cells were markedly increased compared to those of cells incubated with medium alone. However, when amoebae were pretreated with a PI3K inhibitor, wortmannin before being incubated with E. histolytica, E. histolytica-induced PS externalization and DNA fragmentation in Jurkat cells were significantly reduced compared to results for amoebae pretreated with DMSO. In addition, pretreatment of amoebae with a PKC inhibitor, staurosporine strongly inhibited Jurkat T cell death. However, E. histolytica-induced cleavage of caspase-3, -6, and -7 were not inhibited by pretreatment of amoebae with wortmannin or staurosporin. In addition, we found that amoebic PI3K and PKC have an important role on amoeba adhesion to host compartment. These results suggest that amebic PI3K and PKC activation may play an important role in caspase-independent cell death in Entamoeba-induced apoptosis.

Tritrichomonas foetus displays classical detergent-resistant membrane microdomains on its cell surface

Tritrichomonas foetus is a serious veterinary parasite that causes bovine trichomoniasis, a sexually transmitted disease that results in reproductive failure and considerable economic losses in areas that practice natural breeding. T. foetus is an extracellular parasite, which initially adheres to and infects the urogenital tract using a diverse array of surface glycoconjugates, including adhesins and extracellular matrix-binding molecules. However, the cellular mechanisms by which T. foetus colonizes mucosal surfaces and causes tissue damage are not well defined. Several studies have demonstrated the involvement of pathogen or host lipid rafts in cellular events that occur during pathogenesis, including adhesion, invasion and evasion of the immune response. In this study, we demonstrate that detergent-resistant membranes are present in the plasma membrane of T. foetus. We further demonstrate that microdomains are cholesterol-enriched and contain ganglioside GM1-like molecules. In addition, we demonstrate that lipid microdomains do not participate in T. foetus adhesion to host cells. However, the use of agents that disrupt and disorganize the plasma membrane indicated the involvement of the T. foetus lipid microdomains, in cell division and in the formation of endoflagellar forms. Our results suggest that trophozoites and endoflagellar forms present a different plasma membrane organization.

Localization of phosphatidylinositol 4,5-bisphosphate to lipid rafts and uroids in the human protozoan parasite Entamoeba histolytica

Entamoeba histolytica is an intestinal protozoan parasite and is the causative agent of amoebiasis. During invasive infection, highly motile amoebae destroy the colonic epithelium, enter the blood circulation, and disseminate to other organs such as liver, causing liver abscess. Motility is a key factor in E. histolytica pathogenesis, and this process relies on a dynamic actomyosin cytoskeleton. In other systems, phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] is known to regulate a wide variety of cellular functions, including signal transduction, actin remodeling, and cell motility. Little is known about the role of PI(4,5)P2 in E. histolytica pathogenicity. In this study, we demonstrate that PI(4,5)P2 is localized to cholesterol-rich microdomains, lipid rafts, and the actin-rich fractions of the E. histolytica membrane. Microscopy revealed that the trailing edge of polarized trophozoites, uroids, are highly enriched in lipid rafts and their constituent lipid, PI(4,5)P2. Polarization and enrichment of uroids and rafts with PI(4,5)P2 were enhanced upon treatment of E. histolytica cells with cholesterol. Exposure to cholesterol also increased intracellular calcium, which is a downstream effector of PI(4,5)P2, with a concomitant increase in motility. Together, our data suggest that in E. histolytica, PI(4,5)P2 may signal from lipid rafts and cholesterol may play a role in triggering PI(4,5)P2-mediated signaling to enhance the motility of this pathogen.

Sink or swim: lipid rafts in parasite pathogenesis

Lipid rafts, sterol- and sphingolipid-rich membrane microdomains, have been extensively studied in mammalian cells. Recently, lipid rafts have been shown to control virulence in a variety of parasites including Entamoeba histolytica, Giardia intestinalis, Leishmania spp., Plasmodium spp., Toxoplasma gondii, and Trypanosoma spp. Parasite rafts regulate adhesion to host and invasion, and parasite adhesion molecules often localize to rafts. Parasite rafts also control vesicle trafficking, motility, and cell signaling. Parasites disrupt host cell rafts; the dysregulation of host membrane function facilitates the establishment of infection and evasion of the host immune system. Discerning the mechanism by which lipid rafts regulate parasite pathogenesis is essential to our understanding of virulence. Such insight may guide the development of new drugs for disease management.

Common pathways for receptor-mediated ingestion of Escherichia coli and LDL cholesterol by Entamoeba histolytica regulated in part by transmembrane kinase 39

The single-celled parasite, Entamoeba histolytica, is an enteric pathogen that ingests bacteria and host cells. Inhibition of phagocytosis renders the parasite avirulent. The ligand/receptor interactions that allow E. histolytica to phagocytose are not well understood. We hypothesised that E. histolytica trophozoites might accomplish ingestion through the utilisation of a scavenger receptor for cholesterol. Here we show that acetylated low density lipoprotein cholesterol was phagocytosed by amoebae via receptor mediated mechanisms. Acetylated low density lipoprotein cholesterol competitively inhibited by 31 ± 1.3% (P < 0.005) the ingestion of Escherichia coli, but not erythrocytes and Jurkat T lymphocytes, suggesting a partially redundant phagocytic pathway for E. coli and cholesterol. Inducible expression ofa signalling-dead dominant-negative version of E. histolytica transmembrane kinase 39 inhibited ingestion of E. coli by 55 ± 3% (P < 0.005) but not LDL particles. We concluded that ingestion of E. coli was regulated by TMK39 and partially shared the acetylated low density lipoprotein cholesterol uptake pathway.

Exposure to host ligands correlates with colocalization of Gal/GalNAc lectin subunits in lipid rafts and phosphatidylinositol (4,5)-bisphosphate signaling in Entamoeba histolytica

Entamoeba histolytica is an intestinal parasite that causes dysentery and liver abscess. Parasite cell surface receptors, such as the Gal/GalNAc lectin, facilitate attachment to host cells and extracellular matrix. The Gal/GalNAc lectin binds to galactose or N-acetylgalactosamine residues on host components and is composed of heavy (Hgl), intermediate (Igl), and light (Lgl) subunits. Although Igl is constitutively localized to lipid rafts (cholesterol-rich membrane domains), Hgl and Lgl transiently associate with this compartment in a cholesterol-dependent fashion. In this study, trophozoites were exposed to biologically relevant ligands to determine if ligand binding influences the submembrane distribution of the subunits. Exposure to human red blood cells (hRBCs) or collagen, which are bona fide Gal/GalNAc lectin ligands, was correlated with enrichment of Hgl and Lgl in rafts. This enrichment was abrogated in the presence of galactose, suggesting that direct lectin-ligand interactions are necessary to influence subunit location. Using a cell line that is able to attach to, but not phagocytose, hRBCs, it was shown that physical attachment to ligands was not sufficient to induce the enrichment of lectin subunits in rafts. Additionally, the mutant had lower levels of phosphatidylinositol (4,5)-bisphosphate (PIP(2)); PIP(2) loading restored the ability of this mutant to respond to ligands with enrichment of subunits in rafts. Finally, intracellular calcium levels increased upon attachment to collagen; this increase was essential for the enrichment of lectin subunits in rafts. Together, these data provide evidence that ligand-induced enrichment of lectin subunits in rafts may be the first step in a signaling pathway that involves both PIP(2) and calcium signaling.

Localisation to lipid rafts correlates with increased function of the Gal/GalNAc lectin in the human protozoan parasite, Entamoeba histolytica

Entamoeba histolytica is the causative agent of dysentery and liver abscess and is prevalent in developing countries. Adhesion to the host is critical to infection and is mediated by amoebic surface receptors. One such receptor, the Gal/GalNAc lectin, binds to galactose or N-acetylgalactosamine residues on host components and consists of heavy (Hgl), light (Lgl) and intermediate (Igl) subunits. The mechanism by which the lectin assembles into a functional complex is not known. The parasite also relies on cholesterol-rich domains (lipid rafts) for adhesion. Therefore, it is conceivable that rafts regulate the assembly or function of the lectin. To test this, amoebae were loaded with cholesterol and lipid rafts were purified and characterised. Western blotting showed that cholesterol loading resulted in co-compartmentalisation of all three subunits in rafts. This co-compartmentalisation was accompanied by an increase in the ability of the amoebae to bind to host cells in a galactose-specific manner, suggesting that there is a correlation between location and function of the Gal/GalNAc lectin. Cholesterol loading did not increase the surface levels of the lectin subunits. Therefore, the cholesterol-induced increase in adhesion was not the result of externalisation of an internal pool of subunits. A mutant cell line that modestly responded to cholesterol with a slight increase in adhesion exhibited only a slight enrichment of Hgl and Lgl in rafts. This supports the connection between location and function of the Gal/GalNAc lectin. Actin can also influence the interaction of proteins with rafts. Therefore, the sub-membrane distribution of the lectin subunits was also assessed after treatment with an actin depolymerising agent, cytochalasin D. Cytochalasin D-treatment had no effect on the submembrane distribution of the subunits, suggesting that actin does not prevent the association of lectin subunits with rafts in this system. Together, these data provide insight into the molecular mechanisms regulating the location and function of this adhesin.

Ookinete-interacting proteins on the microvillar surface are partitioned into detergent resistant membranes of Anopheles gambiae midguts

Lipid raft microdomains, a component of detergent resistant membranes (DRMs), are routinely exploited by pathogens during host-cell entry. Multiple membrane-surface proteins mediate Plasmodium ookinete invasion of the Anopheles midgut, a critical step in the parasite life cycle that is successfully targeted by transmission-blocking vaccines (TBV). Given that lipid rafts are a common feature of host-pathogen interactions, we hypothesized that they promote the partitioning of midgut surface proteins and thus facilitate ookinete invasion. In support of this hypothesis, we found that five of the characterized Anopheles TBV candidates, including the leading Anopheles TBV candidate, AgAPN1, are present in Anopheles gambiae DRMs. Therefore, to extend the repertoire of putative midgut ligands that can be targeted by TBVs, we analyzed midgut DRMs by tandem mass spectrometry. We identified 1452 proteins including several markers of DRMs. Since glycosylphosphotidyl inositol (GPI)-anchored proteins partition to DRMs, we characterized the GPI subproteome of An. gambiae midgut brush-border microvilli and found that 96.9% of the proteins identified in the GPI-anchored fractions were also present in DRMs. Our study vastly expands the number of candidate malarial TBV targets for subsequent analysis by the broader community and provides an inferred role for midgut plasmalemma microdomains in ookinete cell invasion.

Lipid raft-dependent adhesion of Giardia intestinalis trophozoites to a cultured human enterocyte-like Caco-2/TC7 cell monolayer leads to cytoskeleton-dependent functional injuries

Gardia intestinalis, the aetiological agent of giardiasis, one of the most common intestinal diseases in both developing and developed countries, induces a loss of epithelial barrier function and functional injuries of the enterocyte by mechanisms that remain unknown. Three possible mechanisms have been proposed: (i) Giardia may directly alter the epithelial barrier after a close interaction between the trophozoite and polarized intestinal cells, (ii) intestinal functions may be altered by factors secreted by Giardia including an 'enterotoxin', proteinases and lectins, and (iii) based on mouse studies, a mechanism involving the intervention of activated T lymphocytes. We used fully differentiated cultured human intestinal Caco-2/TC7 cells forming a monolayer and expressing several polarized functions of enterocytes of small intestine to investigate the mechanisms by which G. intestinalis induces structural and functional alterations in the host intestinal epithelium. We first report that adhesion of G. intestinalis at the brush border of enterocyte-like cells involves the lipid raft membrane microdomains of the trophozoite. We report an adhesion-dependent disorganization of the apical F-actin cytoskeleton that, in turn, results in a dramatic loss of distribution of functional brush border-associated proteins, including sucrase-isomaltase (SI), dipeptidylpeptidase IV (DPP IV) and fructose transporter, GLUT5, and a decrease in sucrose enzyme activity in G. intestinalis-infected enterocyte-like cells. We observed that the G. intestinalis trophozoite promotes an adhesion-dependent decrease in transepithelial electrical resistance (TER) accompanied by a rearrangement of functional tight junction (TJ)-associated occludin, and delocalization of claudin-1. Finally, we found that whereas the occludin rearrangement induced by G. intestinalis was related to apical F-actin disorganization, the delocalization of claudin-1 was not.

Invasion mechanisms among emerging food-borne protozoan parasites

Food-borne parasitic diseases, many known to be more prevalent in poor countries with deficient sanitary conditions, are becoming common worldwide. Among the emerging protozoan parasites, the most prominent is Trypanosoma cruzi, rarely reported in the past to be transmitted by the oral route but currently responsible for frequent outbreaks of acute cases of Chagas disease contracted orally and characterized by high mortality. Several other food-borne protozoans considered emerging include the apicomplexans Toxoplasma gondii and Cryptosporidium, as well as Giardia and Entamoeba histolytica. Here, the interactions of these protozoans with the mucosal epithelia of the host are discussed.

Effect of phosphatidylcholine-cholesterol liposomes on Entamoeba histolytica virulence

Trophozoites of Entamoeba histolytica HM-1:IMSS become less virulent after long-term maintenance in axenic cultures. The factors responsible for the loss of virulence during in vitro cultivation remain unclear. However, it is known that in vitro cultivation of amoeba in culture medium supplemented with cholesterol restores their virulence. In this study, we analyzed the effect of adding phosphatidylcholine-cholesterol (PC-Chol) liposomes to the culture medium and evaluated the effect of this lipid on various biochemical and biological functions of E. histolytica HM-1:IMSS in terms of its virulence. The addition of PC-Chol liposomes to the culture medium maintained the virulence of these parasites against hamster liver at the same level as the original virulent E. histolytica strain, even though these amoebae were maintained without passage through hamster liver for 18 months. The trophozoites also showed increased endocytosis, erythrophagocytosis, and carbohydrate residue expression on the amoebic surface. Protease activities were also modified by the presence of cholesterol in the culture medium. These findings indicate the capacity of cholesterol to preserve amoeba virulence and provide an alternative method for the maintenance of virulent E. histolytica trophozoites without the need for in vivo procedures.

A Sequential Model of Host Cell Killing and Phagocytosis by Entamoeba histolytica

The protozoan parasite Entamoeba histolytica is responsible for invasive intestinal and extraintestinal amebiasis. The virulence of Entamoeba histolytica is strongly correlated with the parasite's capacity to effectively kill and phagocytose host cells. The process by which host cells are killed and phagocytosed follows a sequential model of adherence, cell killing, initiation of phagocytosis, and engulfment. This paper presents recent advances in the cytolytic and phagocytic processes of Entamoeba histolytica in context of the sequential model.

Current and future perspectives on the chemotherapy of the parasitic protozoa Trichomonas vaginalis and Entamoeba histolytica

Trichomonas vaginalis and Entamoeba histolytica are clinically important protozoa that affect humans. T. vaginalis produces sexually transmitted infections and E. histolytica is the causative agent of amebic dysentery. Metronidazole, a compound first used to treat T. vaginalis in 1959, is still the main drug used worldwide to treat these pathogens. It is essential to find new biochemical differences in these organisms that could be exploited to develop new antiprotozoal chemotherapeutics. Recent findings associated with T. vaginalis and E. histolytica biochemistry and host–pathogen interactions are surveyed. Knowledge concerning the biochemistry of these parasites is serving to form the foundation for the development of new approaches to control these important human pathogens.