Cyst-Wall-Protein-1 is fundamental for Golgi-like organelle neogenesis and cyst-wall biosynthesis in Giardia lamblia

The proteasome as a drug target for treatment of parasitic diseases

The proteasome is a proteolytically active molecular machine comprising many different protein subunits. It is essential for growth and survival in eukaryotic cells and has long been considered a drug target. Here, we summarize the biology of the proteasome, the early research relating to the development of specific proteasome inhibitors (PIs) for treatment of various cancers, and their translation and eventual evolution as exciting therapies for parasitic diseases. We also highlight the development and adaptation of technologies that have allowed for a deep understanding of the idiosyncrasies of individual parasite proteasomes, as well as the preclinical and clinical advancement of PIs with remarkable therapeutic indices.

Nourseothricin as a novel drug for selection of transgenic Giardia lamblia

Functional gene and protein characterizations in parasitic protists are often limited by their genetic tractability. Despite the development of CRISPR-Cas9-derived or inspired approaches for a handful of protist parasites, the overall genetic tractability of these organisms remains limited. The intestinal parasite Giardia lamblia is one such species, with the added challenge of a paucity of reliable selection markers. To address this limitation, we tested the feasibility of using Nourseothricin as an effective selection agent in Giardia. Here, we report that axenically-grown WB Giardia cells are sensitive to Nourseothricin and that engineering expression of the streptothricin acetyltransferase (SAT-1) gene from Streptomyces rochei in transgenic parasites confers resistance to this antibiotic. Furthermore, we determine that SAT-1-expressing parasites are cross-resistant neither to Neomycin nor Puromycin, which are widely used to select for transgenic parasites. Consequently, we show that Nourseothricin can be used in sequential combination with both Neomycin and Puromycin to select for dual transfection events. This work increases the number of reliable selection agents and markers for Giardia genetic manipulation, expanding the limited molecular toolbox for this species of global medical importance.

Harnessing the power of new genetic tools to illuminate Giardia biology and pathogenesis

Giardia is a prevalent single-celled microaerophilic intestinal parasite causing diarrheal disease and significantly impacting global health. Double diploid (essentially tetraploid) Giardia trophozoites have presented a formidable challenge to the development of molecular genetic tools to interrogate gene function. High sequence divergence and the high percentage of hypothetical proteins lacking homology to proteins in other eukaryotes have limited our understanding of Giardia protein function, slowing drug target validation and development. For more than 25 years, Giardia A and B assemblages have been readily amenable to transfection with plasmids or linear DNA templates. Here, we highlight the utility and power of genetic approaches developed to assess protein function in Giardia, with particular emphasis on the more recent clustered regularly interspaced palindromic repeats/Cas9-based methods for knockdowns and knockouts. Robust and reliable molecular genetic approaches are fundamental toward the interrogation of Giardia protein function and evaluation of druggable targets. New genetic approaches tailored for the double diploid Giardia are imperative for understanding Giardia's unique biology and pathogenesis.

Development of a chemiluminescence assay for detection of Giardia lamblia in canine stool samples

Our Giardia chemiluminescence assay (GCA) detected Giardia antigens in a dose-dependent manner with a limit of detection at 0.46 ng/mL and a signal-to-baseline ratio at 475. In a study of 30 clinic collected canine stool samples, samples were identified as Giardia positive or negative by a standard Giardia II ELISA (TechLab), the GCA had sensitivity of 93.8 % and specificity of 92.9 %. Study on the set of 16 Giardia positive samples showed that all samples displayed higher signal-to-baseline ratio in GCA than they did in a colorimetric ELISA. A dilution analysis of antigen titer showed that for all positive samples, antigen titers in GCA were equal or higher than those in ELISA. The GCA system of chemiluminescence has shown improved capability in detecting Giardia antigens and provided a valid alternative method for researchers and for laboratories.

Conserved Candidate Antigens and Nanoparticles to Develop Vaccine against Giardia intestinalis

Giardia intestinalis (Giardia lambia, Giardia duodenalis) infections in humans may be asymptomatic or symptomatic and associated with diarrhea (without blood), abdominal cramps, bloating, flatulence, and weight loss. The protozoan Giardia is the third most common cause of diarrhea and death in children under five, preceded only by rotavirus and by Cryptosporidium parvum and C. hominis infections. Antimicrobial drugs, particularly 5-nitroimidazole (5-NIs), are used to treat giardiasis in humans. Immunologically naive or immunocompromised host are more vulnerable to Giardia infection, whereas a degree of resistance to this protozoan is present in humans living in endemic areas. This suggests that vaccination may be a potential and appropriate means to control this parasitic disease outbreak and protect the human population. This review discusses Giardia antigens related to vaccine development. Additionally, based on the latest development of nanoparticle technology, a combination of methods for future research and development is proposed for the design of the next generation of powerful immunogens and an effective vaccine against Giardia.

Identification of target genes regulated by encystation-induced transcription factor Myb2 using knockout mutagenesis in Giardia lamblia

BACKGROUND

Encystation is one of the two processes comprising the life cycle of Giardia lamblia, a protozoan pathogen with tetraploid genome. Giardia lamblia Myb2 (GlMyb2) is a distinct encystation-induced transcription factor whose binding sites are found in the promoter regions of many encystation-induced genes, including its own.

METHODS

Two sequential CRISPR/Cas9 experiments were performed to remove four glmyb2 alleles. The expression level of G. lamblia cyst wall protein 1 (GlCWP1), a well-known target gene of GlMyb2, was measured via western blotting and immunofluorescence assays. Chromatin immunoprecipitation experiments using anti-GlMyb2 antibodies were performed on the encysting G. lamblia cells. Quantitative real-time PCR was performed to confirm an expression of candidate GlMyb2-regulated genes by comparing the transcript level for each target candidate in wild-type and knockout mutant Giardia. The promoter region of glcwp1 was analyzed via deletion and point mutagenesis of the putative GlMyb2 binding sites in luciferase reporters.

RESULTS

Characterization of the null glmyb2 mutant indicated loss of functions related to encystation, i.e. cyst formation, and expression of GlCWP1. The addition of the wild-type glmyb2 gene to the null mutant restored the defects in encystation. Chromatin immunoprecipitation experiments revealed dozens of target genes. Nineteen genes were confirmed as GlMyb2 regulons, which include the glmyb2 gene, six for cyst wall proteins, five for signal transduction, two for transporter, two for metabolic enzymes, and three with unknown functions. Detailed analysis on the promoter region of glcwp1 defined three GlMyb2 binding sites important in its encystation-induced expression.

CONCLUSIONS

Our data confirm that GlMyb2 acts as a transcription activator especially during encystation by comparing the glmyb2 knockout mutant with the wild type. Further investigation using glmyb2 null mutant will provide knowledge regarding transcriptional apparatus required for the encystation process of G. lamblia.

Efficient CRISPR/Cas9-mediated gene disruption in the tetraploid protist Giardia intestinalis

CRISPR/Cas9-mediated genome editing has become an extremely powerful technique used to modify gene expression in many organisms, including parasitic protists. Giardia intestinalis, a protist parasite that infects approximately 280 million people around the world each year, has been eluding the use of CRISPR/Cas9 to generate knockout cell lines due to its tetraploid genome. In this work, we show the ability of the in vitro assembled CRISPR/Cas9 components to successfully edit the genome of G. intestinalis. The cell line that stably expresses Cas9 in both nuclei of G. intestinalis showed effective recombination of the cassette containing the transcription units for the gRNA and the resistance marker. This highly efficient process led to the removal of all gene copies at once for three independent experimental genes, mem, cwp1 and mlf1. The method was also applicable to incomplete disruption of the essential gene, as evidenced by significantly reduced expression of tom40. Finally, testing the efficiency of Cas9-induced recombination revealed that homologous arms as short as 150 bp can be sufficient to establish a complete knockout cell line in G. intestinalis.

Activity of the Giardia intestinalis proteasome during encystation and its connection with the expression of the cyst wall protein 1 (CWP1)

Giardia is a parasite whose life cycle is composed of two stages: replicative trophozoites, responsible for the symptoms of the disease, and infective cysts, resistant to adverse environments outside of hosts. Proteasomes are multicatalytic peptidase complexes responsible for the specific degradation of proteins in eukaryotic cells. This study assessed the proteasome activity in the trophozoite and during encystation. Strong activation of the proteasome was observed during the differentiation of trophozoites into cysts, reaching its maximum level 24 h after the stimulus. We also found that the Giardia proteasome presents unusual characteristics related to higher eukaryotic proteasomes, making it an eventual therapeutic target. Here we tested the effects on the synthesis of a cyst wall protein by chemical inactivation of the proteasome and by overexpression or partial inhibition of the deubiquitinating protein RPN11 in transfected cells. Moreover, an analysis of the intracellular localization of RPN11 (an integral part of the proteasome regulatory particle) revealed major changes associated with the differentiation of trophozoites into cysts. This evidence further supports the important role of the proteasome in Giardia encystation.

The reduced ARF regulatory system in Giardia intestinalis pre-dates the transition to parasitism in the lineage Fornicata

Giardia intestinalis is an enteric pathogen with an extremely modified membrane trafficking system, lacking canonical compartments such as the Golgi, endosomes, and intermediate vesicle carriers. By comparison the fornicate relatives of Giardia possess greater endomembrane system complexity. In eukaryotes, the ADP ribosylation factor (ARF) GTPase regulatory system proteins, which consist of the small GTPase ARF1, and its guanine exchange nucleotide factors (GEFs) and GTPase activating proteins (GAPs), coordinate temporal and directional trafficking of cargo vesicles by recognizing and interacting with heterotetrameric coat complexes at pre-Golgi and post-Golgi interfaces. To understand the evolution of this regulatory system across the fornicate lineage, we have performed comparative genomic and phylogenetic analyses of the ARF GTPases, and their regulatory GAPs and GEFs in fornicate genomes and transcriptomes. Prior to our analysis of the fornicates, we first establish that the ARF GAP sub-family ArfGAP with dual PH domains (ADAP) is sparsely distributed but present in at least four eukaryotic supergroups and thus was likely present in the Last Eukaryotic Common Ancestor (LECA). Next, our collective comparative genomic and phylogenetic investigations into the ARF regulatory proteins in fornicates identify a duplication of ARF1 GTPase yielding two paralogues of ARF1F proteins, ancestral to all fornicates and present in all examined isolates of Giardia. However, the ARF GEF and ARF GAP complement is reduced compared with the LECA. This investigation shows that the system was significantly streamlined prior to the fornicate ancestor but was not further reduced concurrent with a transition into a parasitic lifestyle.

Giardia intestinalis can interact, change its shape and internalize large particles and microorganisms

Giardia intestinalis is a parasitic protozoan that inhabits its vertebrate hosts' upper small intestine and is the most common cause of waterborne diarrhoea worldwide. Giardia trophozoites present few organelles, and among them, they possess peripheral vesicles (PVs), which are considered an endosomal-lysosomal system. All experimental procedures carried out until now indicate that Giardia ingests macromolecules by fluid-phase and receptor-mediated endocytic pathways. Still, there is no description concerning the interaction and ingestion of large materials. Here, we tested Giardia's capacity to interact with large particles; once, in vivo, it inhabits an environment with a microbiota. We tested protozoan interaction with yeasts, bacteria, latex beads, ferritin and albumin, in different times of interaction and used several microscopy techniques (light microscopy, scanning electron microscopy and transmission electron microscopy) to follow their fate. Giardia interacted with all of the materials we tested. Projections of the plasma membrane similar to pseudopods were seen. As albumin, small markers were found in the PVs while the larger materials were not seen there. Large vacuoles containing large latex beads were detected intracellularly. Thus, we observed that: (1) Giardia interacts with large materials; (2) Giardia can display an amoeboid shape and exhibit membrane projections when in contact with microorganisms and large inorganic materials; (3) the region of the exit of the ventral flagella is very active when in contact with large materials, although all cell surface also present activity in the interactions; (4) intracellular vacuoles, which are not the PVs, present ingested large beads.

Golgi apparatus components in Entamoeba histolytica and Entamoeba dispar after monensin treatment

Highly dynamic ribosomes, glycogen granules, thinly fibrillar material, and multiple membrane-bound vesicles are embedded in the matrix-rich cytoplasm of Entamoeba spp. trophozoites. The absence of a Golgi apparatus in these amoebae has been commonly accepted. Here we challenge this observation by incubating Entamoeba histolytica and Entamoeba dispar with monensin, an ionophore that produces swelling of the Golgi apparatus. We observe changes in the trophozoites through standard transmission electron microscopy, cryofixation and cryosubstitution, and analyze the label and expression of known resident proteins of the cis-GM130 and trans-TGN38 Golgi network through confocal microscopy and Western blot assays. Cryosubstitution and standard methods using the treatment, preserved membranous lamellae resembling Golgi components. GM130 and TGN38 Golgi antigens were found by immunoelectron, immunoblot, and co-localization by confocal microscopy using the reagent NBD C6-ceramide. Our results indicate that previously undetected Golgi apparatus components are present in the cytoplasm of E. histolytica and E. dispar.

Human intestinal parasitic infection: a narrative review on global prevalence and epidemiological insights on preventive, therapeutic and diagnostic strategies for future perspectives

INTRODUCTION

Intestinal parasitic infection (IPI) is a global health concern among socioeconomically deprived communities in many developing countries. Many preventative strategies have been deployed to control IPI, however, there is a lack in standards on the techniques used to diagnose and monitor the prevalence of IPI.

AREAS COVERED

The present article will review the diseases associated with IPI and discuss the current IPI control strategies such as the water, sanitation, and hygiene (WASH) interventions, community-led total sanitation (CLTS) approach, and regular anthelminthic treatments. For the first time, this review will also evaluate all currently practised diagnostic techniques for the detection of intestinal parasites and provide insights on future IPI control strategies.

EXPERT OPINION

Advanced and improved diagnostic methods such as qPCR coupled with a high-resolution melting curve, aptamers, biosensors, and detection of extracellular vesicles can be used for detection of IPI. Vaccination against intestinal parasites can be made available to increase antibodies to interfere with the blood-feeding process by the parasites, which subsequently reduces the reproductive rates of the parasites. These methods collectively can serve as future management strategies for intestinal parasitic infections.

Anti-Giardia Drug Discovery: Current Status and Gut Feelings

Giardia parasites are ubiquitous protozoans of global importance that impact a wide range of animals including humans. They are the most common enteric pathogen of cats and dogs in developed countries and infect ∼1 billion people worldwide. While Giardia infections can be asymptomatic, they often result in severe and chronic diseases. There is also mounting evidence that they are linked to postinfection disorders. Despite growing evidence of the widespread morbidity associated with Giardia infections, current treatment options are limited to compound classes with broad antimicrobial activity. Frontline anti-Giardia drugs are also associated with increasing drug resistance and treatment failures. To improve the health and well-being of millions, new selective anti-Giardia drugs are needed alongside improved health education initiatives. Here we discuss current treatment options together with recent advances and gaps in drug discovery. We also propose criteria to guide the discovery of new anti-Giardia compounds.

Phosphoinositide-binding proteins mark, shape and functionally modulate highly-diverged endocytic compartments in the parasitic protist Giardia lamblia

Phosphorylated derivatives of phosphatidylinositol (PIPs) are key membrane lipid residues involved in clathrin-mediated endocytosis (CME). CME relies on PIP species PI(4,5)P₂ to mark endocytic sites at the plasma membrane (PM) associated to clathrin-coated vesicle (CCV) formation. The highly diverged parasitic protist Giardia lamblia presents disordered and static clathrin assemblies at PM invaginations, contacting specialized endocytic organelles called peripheral vacuoles (PVs). The role for clathrin assemblies in fluid phase uptake and their link to internal membranes via PIP-binding adaptors is unknown. Here we provide evidence for a robust link between clathrin assemblies and fluid-phase uptake in G. lamblia mediated by proteins carrying predicted PX, FYVE and NECAP1 PIP-binding modules. We show that chemical and genetic perturbation of PIP-residue binding and turnover elicits novel uptake and organelle-morphology phenotypes. A combination of co-immunoprecipitation and in silico analysis techniques expands the initial PIP-binding network with addition of new members. Our data indicate that, despite the partial conservation of lipid markers and protein cohorts known to play important roles in dynamic endocytic events in well-characterized model systems, the Giardia lineage presents a strikingly divergent clathrin-centered network. This includes several PIP-binding modules, often associated to domains of currently unknown function that shape and modulate fluid-phase uptake at PVs.

In well-characterized model eukaryotes, clathrin-mediated endocytosis is a key process for uptake of extracellular material and is regulated by more than 50 known proteins. A large number of these carry phosphoinositide (PIP)-binding domains and play a central role in the regulation of endocytosis. Here, we report on the detailed functional characterization of PIP-binding proteins in the intestinal parasitic protist Giardia lamblia. We show evidence that proteins carrying specific PIP-binding domains are directly involved in fluid-phase uptake. Furthermore, using co-immunoprecipitation assays, we confirm these proteins’ association to G. lamblia’s clathrin assemblies. In addition, using state-of-the-art imaging strategies, we demonstrate a previously unappreciated level of complexity involving PIPs and their partner proteins in marking and shaping G. lamblia’s unique endocytic compartments. Our data contribute substantially to an updated working model for G. lamblia’s host-parasite interface, demonstrating how uptake in this parasite is directly regulated by a variety of PIP residues and PIP-binding modules, which have been re-routed from conserved pathways, likely as a result of host-parasite co-evolution.

Recent advances in functional research in Giardia intestinalis

This review considers current advances in tools to investigate the functional biology of Giardia, it's coding and non-coding genes, features and cellular and molecular biology. We consider major gaps in current knowledge of the parasite and discuss the present state-of-the-art in its in vivo and in vitro cultivation. Advances in in silico tools, including for the modelling non-coding RNAs and genomic elements, as well as detailed exploration of coding genes through inferred homology to model organisms, have provided significant, primary level insight. Improved methods to model the three-dimensional structure of proteins offer new insights into their function, and binding interactions with ligands, other proteins or precursor drugs, and offer substantial opportunities to prioritise proteins for further study and experimentation. These approaches can be supplemented by the growing and highly accessible arsenal of systems-based methods now being applied to Giardia, led by genomic, transcriptomic and proteomic methods, but rapidly incorporating advanced tools for detection of real-time transcription, evaluation of chromatin states and direct measurement of macromolecular complexes. Methods to directly interrogate and perturb gene function have made major leaps in recent years, with CRISPr-interference now available. These approaches, coupled with protein over-expression, fluorescent labelling and in vitro and in vivo imaging, are set to revolutionize the field and herald an exciting time during which the field may finally realise Giardia's long proposed potential as a model parasite and eukaryote.

Development of CRISPR/Cas9-mediated gene disruption systems in Giardia lamblia

Giardia lamblia becomes dormant by differentiation into a water-resistant cyst that can infect a new host. Synthesis of three cyst wall proteins (CWPs) is the fundamental feature of this differentiation. Myeloid leukemia factor (MLF) proteins are involved in cell differentiation, and tumorigenesis in mammals, but little is known about its role in protozoan parasites. We developed a CRISPR/Cas9 system to understand the role of MLF in Giardia. Due to the tetraploid genome in two nuclei of Giardia, it could be hard to disrupt a gene completely in Giardia. We only generated knockdown but not knockout mutants. We found that knockdown of the mlf gene resulted in a significant decrease of cwp gene expression and cyst formation, suggesting a positive role of MLF in encystation. We further used mlf as a model gene to improve the system. The addition of an inhibitor for NHEJ, Scr7, or combining all cassettes for gRNA and Cas9 expression into one plasmid resulted in improved gene disruption efficiencies and a significant decrease in cwp gene expression. Our results provide insights into a positive role of MLF in inducing Giardia differentiation and a useful tool for studies in Giardia.

A cytonaut's guide to protein trafficking in Giardia lamblia

Over the past years, the subcellular organization of the Excavata member Giardia lamblia (syn. duodenalis, intestinalis) has been investigated in considerable detail. There are several reasons for this endeavour which go beyond this parasite's medical importance and are mostly concerned with its reduced subcellular complexity and debated evolutionary status. One may say that simplification has emerged as a paradigm for the evolution of Giardia's subcellular architecture. However, a complete appreciation of the evolutionary and ecological significance of this phenomenon is far from complete. In this chapter, we present and discuss the most recent data on the main trafficking pathways in G. lamblia which include endo- and exo-cytosis, organellar import and function. We provide perspectives on open questions concerning organelle replication and inheritance and include a technical outlook on methods and approaches to genetic manipulations in G. lamblia. A better understanding of G. lamblia subcellular organization at the morphological and molecular level complements any effort aimed at elucidating this parasitic species' evolutionary status and could provide us with the basis for novel strategies to interfere with parasite transmission and/or pathogenesis.

Robust and stable transcriptional repression in Giardia using CRISPRi

Giardia lamblia is a binucleate protistan parasite causing significant diarrheal disease worldwide. An inability to target Cas9 to both nuclei, combined with the lack of nonhomologous end joining and markers for positive selection, has stalled the adaptation of CRISPR/Cas9-mediated genetic tools for this widespread parasite. CRISPR interference (CRISPRi) is a modification of the CRISPR/Cas9 system that directs catalytically inactive Cas9 (dCas9) to target loci for stable transcriptional repression. Using a Giardia nuclear localization signal to target dCas9 to both nuclei, we developed efficient and stable CRISPRi-mediated transcriptional repression of exogenous and endogenous genes in Giardia. Specifically, CRISPRi knockdown of kinesin-2a and kinesin-13 causes severe flagellar length defects that mirror defects with morpholino knockdown. Knockdown of the ventral disk MBP protein also causes severe structural defects that are highly prevalent and persist in the population more than 5 d longer than defects associated with transient morpholino-based knockdown. By expressing two guide RNAs in tandem to simultaneously knock down kinesin-13 and MBP, we created a stable dual knockdown strain with both flagellar length and disk defects. The efficiency and simplicity of CRISPRi in polyploid Giardia allows rapid evaluation of knockdown phenotypes and highlights the utility of CRISPRi for emerging model systems.

Recent advances in the genomic and molecular biology of Giardia

Giardia duodenalis is the most common gastrointestinal protozoan parasite of humans and a significant contributor to the global burden of both diarrheal disease and post-infectious chronic disorders. Robust tools for analyzing gene function in this parasite have been developed and a range of genetic tools are now available. These together with public databases have provided insights on the function of different genes in Giardia. In this review we provide a current perspective on different molecular aspects of Giardia related to genomics, regulation of encystation, trophozoite transcriptional responses to physiological and xenobiotic (drug-induced) stress, and mechanisms of drug resistance. We also examine recent insights that have contributed to gain knowledge in the study of VSPs, antigenic variation, epigenetics, DNA repair and in the direct manipulation of gene function in Giardia, with a particular focus on the inducible Cre/loxP system.

Transcriptomic Profiling of High-Density Giardia Foci Encysting in the Murine Proximal Intestine

Giardia is a highly prevalent, understudied protistan parasite causing significant diarrheal disease worldwide. Its life cycle consists of two stages: infectious cysts ingested from contaminated food or water sources, and motile trophozoites that colonize and attach to the gut epithelium, later encysting to form new cysts that are excreted into the environment. Current understanding of parasite physiology in the host is largely inferred from transcriptomic studies using Giardia grown axenically or in co-culture with mammalian cell lines. The dearth of information about the diversity of host-parasite interactions occurring within distinct regions of the gastrointestinal tract has been exacerbated by a lack of methods to directly and non-invasively interrogate disease progression and parasite physiology in live animal hosts. By visualizing Giardia infections in the mouse gastrointestinal tract using bioluminescent imaging (BLI) of tagged parasites, we recently showed that parasites colonize the gut in high-density foci. Encystation is initiated in these foci throughout the entire course of infection, yet how the physiology of parasites within high-density foci in the host gut differs from that of cells in laboratory culture is unclear. Here we use BLI to precisely select parasite samples from high-density foci in the proximal intestine to interrogate in vivo Giardia gene expression in the host. Relative to axenic culture, we noted significantly higher expression (>10-fold) of oxidative stress, membrane transporter, and metabolic and structural genes associated with encystation in the high-density foci. These differences in gene expression within parasite foci in the host may reflect physiological changes associated with high-density growth in localized regions of the gut. We also identified and verified six novel cyst-specific proteins, including new components of the cyst wall that were highly expressed in these foci. Our in vivo transcriptome data support an emerging view that parasites encyst early in localized regions in the gut, possibly as a consequence of nutrient limitation, and also impact local metabolism and physiology.