Proteomic Study of Entamoeba histolytica Trophozoites, Cysts, and Cyst-Like Structures

Pathogenicity and virulence of Entamoeba histolytica, the agent of amoebiasis

The amoeba parasite Entamoeba histolytica is the causative agent of human amebiasis, an enteropathic disease affecting millions of people worldwide. This ancient protozoan is an elementary example of how parasites evolve with humans, e.g. taking advantage of multiple mechanisms to evade immune responses, interacting with microbiota for nutritional and protective needs, utilizing host resources for growth, division, and encystation. These skills of E. histolytica perpetuate the species and incidence of infection. However, in 10% of infected cases, the parasite turns into a pathogen; the host-parasite equilibrium is then disorganized, and the simple lifecycle based on two cell forms, trophozoites and cysts, becomes unbalanced. Trophozoites acquire a virulent phenotype which, when non-controlled, leads to intestinal invasion with the onset of amoebiasis symptoms. Virulent E. histolytica must cross mucus, epithelium, connective tissue and possibly blood. This highly mobile parasite faces various stresses and a powerful host immune response, with oxidative stress being a challenge for its survival. New emerging research avenues and omics technologies target gene regulation to determine human or parasitic factors activated upon infection, their role in virulence activation, and in pathogenesis; this research bears in mind that E. histolytica is a resident of the complex intestinal ecosystem. The goal is to eradicate amoebiasis from the planet, but the parasitic life of E. histolytica is ancient and complex and will likely continue to evolve with humans. Advances in these topics are summarized here.

A multi-epitope based vaccine against the surface proteins expressed in cyst and trophozoite stages of parasite Entamoeba histolytica

Entamoeba histolytica, an anaerobic parasite, infects humans and other primates and causes fatal diseases, such as amebiasis, amebic liver abscesses, and many others. Thousands of people are infected and dying due to the need for a proper protective cure, especially in poor sanitizing regions, such as Latin America, Asia, and Africa. Around 10% of the world population is infected by E. histolytica every year. Consequently, novel preventive approaches are required to eliminate the threats of the parasite. A designed vaccine targeting the exposed proteins that are common between cyst and trophozoite stages of the parasite's life cycle would be an effective way to repress the impact of the parasite. Therefore, an in silico bioinformatics approach was performed to design an effective vaccine targeting surface proteins common between both stages of the parasite's life cycle using B-cell and T-cell epitopes. The epitopes derived from the conserved portions of the proteins and their corresponding isomers specific to the parasite suggested that the vaccine could benefit cross-protection. Furthermore, the three-dimensional structure of the designed vaccine was modelled, refined, and validated using multiple bioinformatics tools. The physiological properties and solubility were also predicted using different algorithmic tools and found to be highly soluble in nature. The vaccine was found interactcted with TLR immune receptors, and the stability was observed via dynamics simulation. Codon optimization and cloning were performed for expression analysis. Immune simulation prediction anticipated significant immune responses with a high IgG and IgM antibodies expression, Th and Tc cells population, B-cell population, memory cells, INF-γ, and IL-2 cytokines. Therefore, the constructed multi-epitope putative vaccine can effectively neutralize the parasite's harmful effects.

Hypothetical proteins play a role in stage conversion, virulence, and the stress response in the Entamoeba species

Entamoeba histolytica is a protozoan parasite that causes amoebic dysentery and amoebic liver abscess in humans, affecting millions of people worldwide. This pathogen possesses a two-stage life cycle consisting of an environmentally stable cyst and a pathogenic amoeboid trophozoite. As cysts can be ingested from contaminated food and water, this parasite is prevalent in underdeveloped countries and poses a significant health burden. Until recently there was no reliable method for inducing stage conversion in E. histolytica in vitro. As such, the reptilian pathogen, Entamoeba invadens, has long-served as a surrogate. Much remains unclear about stage conversion in these parasites and current treatments for amoebiasis are lacking, as they cause severe side effects. Therefore, new therapeutic strategies are needed. The genomes of these parasites remain enigmatic as approximately 54% of E. histolytica genes and 66% of E. invadens genes are annotated as hypothetical proteins. In this study, we characterized two hypothetical proteins in the Entamoeba species, EIN_059080, in E. invadens, and its homolog, EHI_056700, in the human pathogen, E. histolytica. EHI_056700 has no homolog in the human host. We used an RNAi-based silencing system to reduce expression of these genes in E. invadens and E. histolytica trophozoites. Loss of EIN_059080 resulted in a decreased rate of encystation and an increased rate of erythrophagocytosis, an important virulence function. Additionally, mutant parasites were more susceptible to oxidative stress. Similarly, loss of EHI_056700 in E. histolytica trophozoites resulted in increased susceptibility to oxidative stress and glucose deprivation, but not to nitrosative stress. Unlike the E. invadens mutants, E. histolytica parasites with decreased reduced expression of EHI_056700 exhibited a decreased rate of erythrophagocytosis of and adhesion to host cells. Taken together, these data suggest that these hypothetical proteins play a role in stage conversion, virulence, and the response to stress in the Entamoebae. Since parasites with reduced expression of EHI_056700 show decreased virulence functions and increased susceptibility to physiologically relevant stressors, EHI_056700 may represent a possible therapeutic target for the treatment of amoebiasis.

Multi-omics analysis to characterize molecular adaptation of Entamoeba histolytica during serum stress

Entamoeba histolytica is responsible for dysentery and extraintestinal disease in humans. To establish successful infection, it must generate adaptive response against stress due to host defense mechanisms. We have developed a robust proteomics workflow by combining miniaturized sample preparation, low flow-rate chromatography, and ultra-high sensitivity mass spectrometry, achieving increased proteome coverage, and further integrated proteomics and RNA-seq data to decipher regulation at translational and transcriptional levels. Label-free quantitative proteomics led to identification of 2344 proteins, an improvement over the maximum number identified in E. histolytica proteomic studies. In serum-starved cells, 127 proteins were differentially abundant and were associated with functions including antioxidant activity, cytoskeleton, translation, catalysis, and transport. The virulence factor, Gal/GalNAc-inhibitable lectin subunits, was significantly altered. Integration of transcriptomic and proteomic data revealed that only 30% genes were coordinately regulated at both transcriptional and translational levels. Some highly expressed transcripts did not change in protein abundance. Conversely, genes with no transcriptional change showed enhanced protein abundance, indicating post-transcriptional regulation. This multi-omics approach enables more refined gene expression analysis to understand the adaptive response of E. histolytica during growth stress.

Encystation of Entamoeba histolytica in Axenic Culture

Entamoeba histolytica is a parasitic protozoan that causes amoebic dysentery, which affects approximately 90 million people each year worldwide. E. histolytica is transmitted through ingestion of food and water contaminated with the cyst form, which undergoes excystation in the small intestine to the trophozoite form that colonizes the large intestine. The reptile pathogen Entamoeba invadens has served as a model for studying stage conversion between the trophozoite and cyst form due to lack of reproducible encystation of E. histolytica in the laboratory. Although much has been learned about encystation and excystation using E. invadens, the findings do not fully translate to E. histolytica due to the extensive genetic and host differences between these species. Here, we present the first reproducible encystation of E. histolytica in vitro. The cysts produced were viable and displayed the four characteristic hallmarks: round shape, chitinous cell wall, tetranucleation, and detergent resistance. Using flow cytometry analysis, glucose limitation and high cell density were key for encystation, as for E. invadens. Entry into encystation was enhanced by the short-chain fatty acids acetate and propionate, unlike for E. invadens. This new model will now allow the further study of E. histolytica stage conversion, transmission, and treatment.

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.

Proteomic Insights into the Biology of the Most Important Foodborne Parasites in Europe

Foodborne parasitoses compared with bacterial and viral-caused diseases seem to be neglected, and their unrecognition is a serious issue. Parasitic diseases transmitted by food are currently becoming more common. Constantly changing eating habits, new culinary trends, and easier access to food make foodborne parasites' transmission effortless, and the increase in the diagnosis of foodborne parasitic diseases in noted worldwide. This work presents the applications of numerous proteomic methods into the studies on foodborne parasites and their possible use in targeted diagnostics. Potential directions for the future are also provided.

Characterization of Extracellular Vesicles from Entamoeba histolytica Identifies Roles in Intercellular Communication That Regulates Parasite Growth and Development

Extracellular vesicles (EVs) secreted by eukaryotic and prokaryotic cells to transport lipids, proteins, and nucleic acids to the external environment have important roles in cell-cell communication through cargo transfer. We identified and characterized EVs from Entamoeba histolytica, a protozoan parasite and a human pathogen. Conditioned medium from amebic parasites contained particles consistent with the expected size and morphology of EVs. Mass spectrometry was used to characterize the EV proteome and showed that it was enriched in common exosome marker proteins, including proteins associated with vesicle formation, cell signaling, and metabolism, as well as cytoskeletal proteins. Additionally, the EVs were found to selectively package small RNAs (sRNA), which were protected within the vesicles against RNase treatment. Sequencing analysis of the sRNA contained in EVs revealed that the majority were 27 nucleotides (nt) in size and represented a subset of the cellular antisense small RNA population that has previously been characterized in Entamoeba RNA interference (RNAi) pathway proteins, including Argonaute, were also present in amebic EVs. Interestingly, we found that the amebic EVs impacted intercellular communication between parasites and altered encystation efficiency. EVs isolated from encysting parasites promoted encystation in other parasites, whereas EVs from metabolically active trophozoites impeded encystation. Overall, the data reveal that Entamoeba secrete EVs that are similar in size and shape to previously characterized exosomes from other organisms and that these EVs contain a defined protein and small RNA cargo and have roles in intercellular communication among parasites and influence growth kinetics.

Proteomics approaches to understand cell biology and virulence of Entamoeba histolytica protozoan parasite

Entamoeba histolytica is the primitive eukaryotic parasite responsible of human amoebiasis, a disease characterized by bloody intestinal diarrhea and invasive extraintestinal illness. The knowledge of the complete genome sequence of virulent E. histolytica and related non-pathogenic species allowed the development of novel genome-wide methodological approaches including protein expression profiling and cellular proteomics in the so called post-genomic era. Proteomics studies have greatly increased our understanding of the cell biology of this ancient parasite. This review summarizes the current works concerning proteomics studies on cell biology, life cycle, virulence and pathogenesis, novel therapies, and protein expression regulation mechanisms in E. histolytica parasite. Also, we discuss the use of proteomics data for the development of novel therapies, the identification of potential disease biomarkers and differential diagnosis between species. SIGNIFICANCE: Entamoeba histolytica is the unicellular protozoan parasite responsible of human amoebiasis, a serious disease with worldwide distribution characterized by bloody intestinal diarrhea and invasive extraintestinal illness including peritonitis and liver, pulmonary and brain abscesses. The post-genomic era allowed the development of proteomic studies including protein expression profiling and cellular proteomics. These proteomics studies have greatly increased our understanding on cell biology, life cycle (cyst-trophozoite conversion), virulence, pathogenesis, novel therapies, and protein expression regulation mechanisms in E. histolytica. Importantly, proteomics has revealed the identity of proteins related to novel therapies, and the identification of potential disease biomarkers and proteins with use in diagnosis between species. Hopefully in the coming years, and through the use of more sophisticated omics tools, including deep proteomics, a more complete set of proteins involved in the aforementioned cellular processes can be obtained to understand the biology of this ancient eukaryote.

Demonstration and Characterization of Cyst-Like Structures in the Life Cycle of Trichomonas vaginalis

Trichomonas vaginalis is the parasitic protozoan residing in human urogenital tract causing trichomoniasis, which is the leading non-viral sexually transmitted disease. It has cosmopolitan distribution throughout the globe and affects both men and women. Lifecycle of the parasite has been traditionally described as consisting of motile and symptom-causing trophozoites. Chemical and temperature perturbations in trophozoites have been shown to aid conversion to pseudocysts, which is poorly investigated. In the current study, we show the formation of viable cyst-like structures (CLS) in stationary phase of T. vaginalis axenic culture. We used a fluorescent stain called calcofluor white, which specifically binds to chitin and cellulose-containing structures, to score for T. vaginalis CLS. Using flow cytometry, we demonstrated and quantitated the processes of encystation as well as excystation; thus, completing the parasite's lifecycle in vitro without any chemical/temperature alterations. Like cysts from other protozoan parasites such as Entamoeba histolytica and Giardia lamblia, T. vaginalis CLS appeared spherical, immotile, and resistant to osmotic lysis and detergent treatments. Ultrastructure of CLS demonstrated by Transmission Electron Microscopy showed a thick electron-dense deposition along its outer membrane. To probe the physiological role of CLS, we exposed parasites to vaginal pH and observed that trophozoites took this as a cue to convert to CLS. Further, upon co- culturing with cells of cervical origin, CLS rapidly excysted to form trophozoites which abrogated the cervical cell monolayer in a dose-dependent manner. To further corroborate the presence of two distinct forms in T. vaginalis, we performed two-dimensional gel electrophoresis and global, untargeted mass spectrometry to highlight differences in the proteome with trophozoites. Interestingly, CLS remained viable in chlorinated swimming pool water implicating the possibility of its role as environmentally resistant structures involved in non-sexual mode of parasite transmission. Finally, we showed that symptomatic human patient vaginal swabs had both T. vaginalis trophozoites and CLS; thus, highlighting its importance in clinical infections. Overall, our study highlights the plasticity of the pathogen and its rapid adaption when subjected to stressful environmental cues and suggests an important role of CLS in the parasite's life cycle, pathogenesis and transmission.

Horizontal transmission of Endolimax piscium, causative agent of systemic amoebiasis in Senegalese sole Solea senegalensis

Systemic amoebiasis of Senegalese sole Solea senegalensis is caused by Endolimax piscium Constenla, Padrós & Palenzuela, 2014 a cryptic parasitic member of the Archamoebae whose epidemiology is yet unknown. To test whether the parasite can be transmitted horizontally, an experimental trial by cohabitation between non-infected and infected fish was designed. Transmission of the parasite from naturally infected to healthy fish was confirmed in the experiment, with the water as the most likely route of infection. Under the conditions of the study, the infection process was remarkably slow, as parasites could be detected by in situ hybridization within the intestinal mucosa of recipient fish only after 17 wk of cohabitation, and none of the new hosts displayed clinical signs of disease. Long prepatent period and the need for additional triggering factors for the development of the clinical condition are suggested. The intestinal mucosa is proposed as the tissue where the amoeba can survive as endocommensal, but also as an invasion route from which the parasite would disperse to other organs.

Utilization of Different Omic Approaches to Unravel Stress Response Mechanisms in the Parasite Entamoeba histolytica

During its life cycle, the unicellular parasite Entamoeba histolytica is challenged by a wide variety of environmental stresses, such as fluctuation in glucose concentration, changes in gut microbiota composition, and the release of oxidative and nitrosative species from neutrophils and macrophages. The best mode of survival for this parasite is to continuously adapt itself to the dynamic environment of the host. Our ability to study the stress-induced responses and adaptive mechanisms of this parasite has been transformed through the development of genomics, proteomics or metabolomics (omics sciences). These studies provide insights into different facets of the parasite's behavior in the host. However, there is a dire need for multi-omics data integration to better understand its pathogenic nature, ultimately paving the way to identify new chemotherapeutic targets against amebiasis. This review provides an integration of the most relevant omics information on the mechanisms that are used by E. histolytica to resist environmental stresses.

Advancements in Parasite Diagnosis and Challenges in the Management of Parasitic Infections: A Mini Review

Intestinal parasitic infections (IPIs) remain a widespread public health concern causing severe implications in both developed and developing countries. Globally, numerous studies have been carried out ranging from various communities to schoolchildren as well as indigenous communities. The infections are commonly caused by helminths (e.g. Ascaris lumbricoides, Trichuris trichiura and hookworm) and protozoa (e.g. Blastocystis hominis, Cryptosporidium sp., Entamoeba histolytica and Giardia duodenalis). Poor sanitation and poverty are some of the factors associated with IPIs. With the ever-increasing impact of IPIs, newer detection approaches have been developed and studied. The efficacy of diagnostic method is crucial to give an accurate identification of these parasites. Recent developments of diagnostic tools such as serology- and molecular-based assays are assisting the conventional method of microscopy in detecting and further confirming current or past infections and the specific species of parasites. Ongoing investigations in parasitic infections using these advanced tools will provide useful information that will enable the evaluation of the effectiveness of the current control program and thus, assist future planning for improved strategies in eradicating these parasitic infections.

Membrane Trafficking Modulation during Entamoeba Encystation

Entamoeba histolytica is an intestinal parasite that infects 50-100 million people and causes up to 55,000 deaths annually. The transmissive form of E. histolytica is the cyst, with a single infected individual passing up to 45 million cysts per day, making cyst production an attractive target for infection control. Lectins and chitin are secreted to form the cyst wall, although little is known about the underlying membrane trafficking processes supporting encystation. As E. histolytica does not readily form cysts in vitro, we assessed membrane trafficking gene expression during encystation in the closely related model Entamoeba invadens. Genes involved in secretion are up-regulated during cyst formation, as are some trans-Golgi network-to-endosome trafficking genes. Furthermore, endocytic and general trafficking genes are up-regulated in the mature cyst, potentially preserved as mRNA in preparation for excystation. Two divergent dynamin-related proteins found in Entamoeba are predominantly expressed during cyst formation. Phylogenetic analyses indicate that they are paralogous to, but quite distinct from, classical dynamins found in human, suggesting that they may be potential drug targets to block encystation. The membrane-trafficking machinery is clearly regulated during encystation, providing an additional facet to understanding this crucial parasitic process.

Detection and differentiation of Entamoeba histolytica and Entamoeba dispar in clinical samples through PCR-denaturing gradient gel electrophoresis

Amebiasis is one of the twenty major causes of disease in Mexico; however, the diagnosis is difficult due to limitations of conventional microscopy-based techniques. In this study, we analyzed stool samples using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) to differentiate between Entamoeba histolytica (pathogenic) and E. dispar (non-pathogenic). The target for the PCR amplification was a small region (228 bp) of the adh112 gene selected to increase the sensitivity of the test. The study involved 62 stool samples that were collected from individuals with complaints of gastrointestinal discomfort. Of the 62 samples, 10 (16.1%) were positive for E. histolytica while 52 (83.9%) were negative. No sample was positive for E. dispar. These results were validated by nested PCR-RFLP (restriction fragment length polymorphism) and suggest that PCR-DGGE is a promising tool to differentiate among Entamoeba infections, contributing to determine the specific treatment for patients infected with E. histolytica, and therefore, avoiding unnecessary treatment of patients infected with the non-pathogenic E. dispar.