Proteomics of secretory and endocytic organelles in Giardia lamblia

Mlf mediates proteotoxic response via formation of cellular foci for protein folding and degradation in Giardia

Myeloid leukemia factor 1 (Mlf1) was identified as a proto-oncoprotein that affects hematopoietic differentiation in humans. However, its cellular function remains elusive, spanning roles from cell cycle regulation to modulation of protein aggregate formation and participation in ciliogenesis. Given that structurally conserved homologs of Mlf1 can be found across the eukaryotic tree of life, we decided to characterize its cellular role underlying this phenotypic pleiotropy. Using a model of the unicellular eukaryote Giardia intestinalis, we demonstrate that its Mlf1 homolog (GiMlf) mainly localizes to two types of cytosolic foci: microtubular structures, where it interacts with Hsp40, and ubiquitin-rich, membraneless compartments, found adjacent to mitochondrion-related organelles known as mitosomes, containing the 26S proteasome regulatory subunit 4. Upon cellular stress, GiMlf either relocates to the affected compartment or disperses across the cytoplasm, subsequently accumulating into enlarged foci during the recovery phase. In vitro assays suggest that GiMlf can be recruited to membranes through its affinity for signaling phospholipids. Importantly, cytosolic foci diminish in the gimlf knockout strain, which exhibits extensive proteomic changes indicative of compromised proteostasis. Consistent with data from other cellular systems, we propose that Mlf acts in the response to proteotoxic stress by mediating the formation of function-specific foci for protein folding and degradation.

Protozoa-Derived Extracellular Vesicles on Intercellular Communication with Special Emphasis on Giardia lamblia

Parasitic diseases are an important worldwide problem threatening human health and affect millions of people. Acute diarrhea, intestinal bleeding, malabsorption of nutrients and nutritional deficiency are some of the issues related to intestinal parasitic infections. Parasites are experts in subvert the host immune system through different kinds of mechanisms. There are evidences that extracellular vesicles (EVs) have an important role in dissemination of the disease and in modulating the host immune system. Released by almost all types of cells, these nanovesicles are a natural secretory product containing multiple components of interest. The EVs are classified as apoptotic bodies, microvesicles, exosomes, ectosomes, and microparticles, according to their physical characteristics, biochemical composition and cell of origin. Interestingly, EVs play an important role in intercellular communication between parasites as well as with the host cells. Concerning Giardia lamblia, it is known that this parasite release EVs during it life cycle that modulate the parasite growth and adherence as well the immune system of the host. Here we review the recently updates on protozoa EVs, with particular emphasis on the role of EVs released by the flagellate protozoa G. lamblia in cellular communication and its potential for future applications as vaccine, therapeutic agent, drug delivery system and as diagnostic or prognostic biomarker.

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.

Giardia intestinalis coiled-coil cytolinker protein 259 interacts with actin and tubulin

Giardia intestinalis is a human parasite that causes a diarrheal disease in developing countries. G. intestinalis has a cytoskeleton (CSK) composed of microtubules and microfilaments, and the Giardia genome does not code for the canonical CSK-binding proteins described in other eukaryotic cells. To identify candidate actin and tubulin cross-linking proteins, we performed a BLAST analysis of the Giardia genome using a spectraplakins consensus sequence as a query. Based on the highest BLAST score, we selected a 259-kDa sequence designated as a cytoskeleton linker protein (CLP259). The sequence was cloned in three fragments and characterized by immunoprecipitation, confocal microscopy, and mass spectrometry (MS). CLP259 was located in the cytoplasm in the form of clusters of thick rods and colocalized with actin at numerous sites and with tubulin in the median body. Immunoprecipitation followed by mass spectrometry revealed that CLP259 interacts with structural proteins such as giardins, SALP-1, axonemal, and eight coiled-coils. The vesicular traffic proteins detected were Mu adaptin, Vacuolar ATP synthase subunit B, Bip, Sec61 alpha, NSF, AP complex subunit beta, and dynamin. These results indicate that CLP259 in trophozoites is a CSK linker protein for actin and tubulin and could act as a scaffold protein driving vesicular traffic.

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.

Peptidylarginine Deiminase Inhibition Abolishes the Production of Large Extracellular Vesicles From Giardia intestinalis, Affecting Host-Pathogen Interactions by Hindering Adhesion to Host Cells

Giardia intestinalis is a microaerophilic protozoan that is an important etiologic agent of diarrhea worldwide. There is evidence that under diverse conditions, the parasite is capable of shedding extracellular vesicles (EVs) which modulate the physiopathology of giardiasis. Here we describe new features of G. intestinalis EV production, revealing its capacity to shed two different enriched EV populations: large (LEV) and small extracellular vesicles (SEV) and identified relevant adhesion functions associated with the larger population. Proteomic analysis revealed differences in proteins relevant for virulence and host-pathogen interactions between the two EV subsets, such as cytoskeletal and anti-oxidative stress response proteins in LEVS. We assessed the effect of two recently identified inhibitors of EV release in mammalian cells, namely peptidylarginine deiminase (PAD) inhibitor and cannabidiol (CBD), on EV release from Giardia. The compounds were both able to effectively reduce EV shedding, the PAD-inhibitor specifically affecting the release of LEVs and reducing parasite attachment to host cells in vitro. Our results suggest that LEVs and SEVs have a different role in host-pathogen interaction, and that treatment with EV-inhibitors may be a novel treatment strategy for recurrent giardiasis.

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.

The protein 14-3-3: A functionally versatile molecule in Giardia duodenalis

Giardia duodenalis is a cosmopolitan zoonotic protozoan parasite causing giardiasis, one of the most common diarrhoeal diseases in human and animals. Beyond its public health relevance, Giardia represents a valuable and fascinating model microorganism. The deep-branching phylogenetic position of Giardia, its simple life cycle and its minimalistic genomic and cellular organization provide a unique opportunity to define basal and "ancestral" eukaryotic functions. The eukaryotic 14-3-3 protein family represents a distinct example of phosphoserine/phosphothreonine-binding proteins. The extended network of protein-protein interactions established by 14-3-3 proteins place them at the crossroad of multiple signalling pathways that regulate physiological and pathological cellular processes. Despite the remarkable insight on 14-3-3 protein in different organisms, from yeast to humans, so far little attention was given to the study of this protein in protozoan parasites. However, in the last years, research efforts have provided evidences on unique properties of the single 14-3-3 protein of Giardia and on its association in key aspects of Giardia life cycle. In the first part of this chapter, a general overview of the features commonly shared among 14-3-3 proteins in different organisms (i.e. structure, target recognition, mode of action and regulatory mechanisms) is included. The second part focus on the current knowledge on the biochemistry and biology of the Giardia 14-3-3 protein and on the possibility to use this protein as target to propose new strategies for developing innovative antigiardial therapy.

Giardia secretome highlights secreted tenascins as a key component of pathogenesis

Background

Giardia is a protozoan parasite of public health relevance that causes gastroenteritis in a wide range of hosts. Two genetically distinct lineages (assemblages A and B) are responsible for the human disease. Although it is clear that differences in virulence occur, the pathogenesis and virulence of Giardia remain poorly understood.

Results

The genome of Giardia is believed to contain open reading frames that could encode as many as 6000 proteins. By successfully applying quantitative proteomic analyses to the whole parasite and to the supernatants derived from parasite culture of assemblages A and B, we confirm expression of ∼1600 proteins from each assemblage, the vast majority of which are common to both lineages. To look for signature enrichment of secreted proteins, we considered the ratio of proteins in the supernatant compared with the pellet, which defined a small group of enriched proteins, putatively secreted at a steady state by cultured growing trophozoites of both assemblages. This secretome is enriched with proteins annotated to have N-terminal signal peptide. The most abundant secreted proteins include known virulence factors such as cathepsin B cysteine proteases and members of a Giardia superfamily of cysteine-rich proteins that comprise variant surface proteins, high-cysteine membrane proteins, and a new class of virulence factors, the Giardia tenascins. We demonstrate that physiological function of human enteric epithelial cells is disrupted by such soluble factors even in the absence of the trophozoites.

Conclusions

We are able to propose a straightforward model of Giardia pathogenesis incorporating key roles for the major Giardia-derived soluble mediators.

Multiple paralogues of α-SNAP in Giardia lamblia exhibit independent subcellular localization and redistribution during encystation and stress

BACKGROUND

The differently-diverged parasitic protist Giardia lamblia is known to have minimal machinery for vesicular transport. Yet, it has three paralogues of SNAP, a crucial component that together with NSF brings about disassembly of the cis-SNARE complex formed following vesicle fusion to target membranes. Given that most opisthokont hosts of this gut parasite express only one α-SNAP, this study was undertaken to determine whether these giardial SNAP proteins have undergone functional divergence.

RESULTS

All three SNAP paralogues are expressed in trophozoites, encysting trophozoites and cysts. Even though one of them clusters with γ-SNAP sequences in a phylogenetic tree, functional complementation analysis in yeast indicates that all the three proteins are functionally orthologous to α-SNAP. Localization studies showed a mostly non-overlapping distribution of these α-SNAPs in trophozoites, encysting cells and cysts. In addition, two of the paralogues exhibit substantial subcellular redistribution during encystation, which was also seen following exposure to oxidative stress. However, the expression of the three genes remained unchanged during this redistribution process. There is also a difference in the affinity of each of these α-SNAP paralogues for GlNSF.

CONCLUSIONS

None of the genes encoding the three α-SNAPs are pseudogenes and the encoded proteins are likely to discharge non-redundant functions in the different morphological states of G. lamblia. Based on the difference in the interaction of individual α-SNAPs with GlNSF and their non-overlapping pattern of subcellular redistribution during encystation and under stress conditions, it may be concluded that the three giardial α-SNAP paralogues have undergone functional divergence. Presence of one of the giardial α-SNAPs at the PDRs of flagella, where neither GlNSF nor any of the SNAREs localize, indicates that this α-SNAP discharges a SNARE-independent role in this gut pathogen.

Membrane-Associated Proteins in Giardia lamblia

The manner in which membrane-associated proteins interact with the membrane defines their subcellular fate and function. This interaction relies on the characteristics of the proteins, their journey after synthesis, and their interaction with other proteins or enzymes. Understanding these properties may help to define the function of a protein and also the role of an organelle. In the case of microorganisms like protozoa parasites, it may help to understand singular features that will eventually lead to the design of parasite-specific drugs. The protozoa parasite Giardia lamblia is an example of a widespread parasite that has been infecting humans and animals from ancestral times, adjusting itself to the changes of the environment inside and outside the host. Several membrane-associated proteins have been posted in the genome database GiardiaDB, although only a few of them have been characterized. This review discusses the data regarding membrane-associated proteins in relationship with lipids and specific organelles and their implication in the discovery of anti-giardial therapies.

"Omic" investigations of protozoa and worms for a deeper understanding of the human gut "parasitome"

The human gut has been continuously exposed to a broad spectrum of intestinal organisms, including viruses, bacteria, fungi, and parasites (protozoa and worms), over millions of years of coevolution, and plays a central role in human health. The modern lifestyles of Western countries, such as the adoption of highly hygienic habits, the extensive use of antimicrobial drugs, and increasing globalisation, have dramatically altered the composition of the gut milieu, especially in terms of its eukaryotic “citizens.” In the past few decades, numerous studies have highlighted the composition and role of human intestinal bacteria in physiological and pathological conditions, while few investigations exist on gut parasites and particularly on their coexistence and interaction with the intestinal microbiota. Studies of the gut “parasitome” through “omic” technologies, such as (meta)genomics, transcriptomics, proteomics, and metabolomics, are herein reviewed to better understand their role in the relationships between intestinal parasites, host, and resident prokaryotes, whether pathogens or commensals. Systems biology–based profiles of the gut “parasitome” under physiological and severe disease conditions can indeed contribute to the control of infectious diseases and offer a new perspective of omics-assisted tropical medicine.

The single cyclic nucleotide-specific phosphodiesterase of the intestinal parasite Giardia lamblia represents a potential drug target

Background

Giardiasis is an intestinal infection correlated with poverty and poor drinking water quality, and treatment options are limited. According to the Center for Disease Control and Prevention, Giardia infections afflict nearly 33% of people in developing countries, and 2% of the adult population in the developed world. This study describes the single cyclic nucleotide-specific phosphodiesterase (PDE) of G. lamblia and assesses PDE inhibitors as a new generation of anti-giardial drugs.

Methods

An extensive search of the Giardia genome database identified a single gene coding for a class I PDE, GlPDE. The predicted protein sequence was analyzed in-silico to characterize its domain structure and catalytic domain. Enzymatic activity of GlPDE was established by complementation of a PDE-deficient Saccharomyces cerevisiae strain, and enzyme kinetics were characterized in soluble yeast lysates. The potency of known PDE inhibitors was tested against the activity of recombinant GlPDE expressed in yeast and against proliferating Giardia trophozoites. Finally, the localization of epitope-tagged and ectopically expressed GlPDE in Giardia cells was investigated.

Results

Giardia encodes a class I PDE. Catalytically important residues are fully conserved between GlPDE and human PDEs, but sequence differences between their catalytic domains suggest that designing Giardia-specific inhibitors is feasible. Recombinant GlPDE hydrolyzes cAMP with a K_m of 408 μM, and cGMP is not accepted as a substrate. A number of drugs exhibit a high degree of correlation between their potency against the recombinant enzyme and their inhibition of trophozoite proliferation in culture. Epitope-tagged GlPDE localizes as dots in a pattern reminiscent of mitosomes and to the perinuclear region in Giardia.

Conclusions

Our data strongly suggest that inhibition of G. lamblia PDE activity leads to a profound inhibition of parasite proliferation and that GlPDE is a promising target for developing novel anti-giardial drugs.

Cellular signaling by the cyclic nucleotides cAMP and cGMP is ubiquitously found in organisms from human to unicellular parasites. Cyclic nucleotide-specific phosphodiesterases (PDEs) are pivotal regulators of these signaling processes and these enzymes represent important drug targets for a variety of diseases. Eleven PDE families are distinguished in humans and selective inhibition of a single human PDE family without targeting others is feasible. In parasites, interference in the signaling mechanism by PDE inhibition may be fatal. The diarrhea-causing parasite Giardia lamblia contains only one single PDE, named GlPDE. GlPDE activity is highly impaired by a range of PDE inhibitors, which also suppress parasite proliferation in vitro. Thus, there is a good agreement between PDE inhibition and parasite drug susceptibility. We demonstrate molecular differences between human PDEs and GlPDE that can be exploited for the development of GlPDE-selective inhibitors. Finally, our data may suggest localization of GlPDE to mitosome organelles, which are absent in human cells and thus are in the focus as possible targets for the treatment of giardiasis. This may add to the notion that GlPDE represents a potential target for the development of novel anti-giardial drugs.

An Interactome-Centered Protein Discovery Approach Reveals Novel Components Involved in Mitosome Function and Homeostasis in Giardia lamblia

Protozoan parasites of the genus Giardia are highly prevalent globally, and infect a wide range of vertebrate hosts including humans, with proliferation and pathology restricted to the small intestine. This narrow ecological specialization entailed extensive structural and functional adaptations during host-parasite co-evolution. An example is the streamlined mitosomal proteome with iron-sulphur protein maturation as the only biochemical pathway clearly associated with this organelle. Here, we applied techniques in microscopy and protein biochemistry to investigate the mitosomal membrane proteome in association to mitosome homeostasis. Live cell imaging revealed a highly immobilized array of 30–40 physically distinct mitosome organelles in trophozoites. We provide direct evidence for the single giardial dynamin-related protein as a contributor to mitosomal morphogenesis and homeostasis. To overcome inherent limitations that have hitherto severely hampered the characterization of these unique organelles we applied a novel interaction-based proteome discovery strategy using forward and reverse protein co-immunoprecipitation. This allowed generation of organelle proteome data strictly in a protein-protein interaction context. We built an initial Tom40-centered outer membrane interactome by co-immunoprecipitation experiments, identifying small GTPases, factors with dual mitosome and endoplasmic reticulum (ER) distribution, as well as novel matrix proteins. Through iterative expansion of this protein-protein interaction network, we were able to i) significantly extend this interaction-based mitosomal proteome to include other membrane-associated proteins with possible roles in mitosome morphogenesis and connection to other subcellular compartments, and ii) identify novel matrix proteins which may shed light on mitosome-associated metabolic functions other than Fe-S cluster biogenesis. Functional analysis also revealed conceptual conservation of protein translocation despite the massive divergence and reduction of protein import machinery in Giardia mitosomes.

Organelles with endosymbiotic origin are present in virtually all extant eukaryotes and have undergone considerable remodeling during > 1 billion years of evolution. Highly diverged organelles such as mitosomes or plastids in some parasitic protozoa are the product of extensive secondary reduction. They are sufficiently unique to generate interest as targets for pharmacological intervention, in addition to providing a rich ground for evolutionary cell biologists. The so-called mitochondria-related organelles (MROs) comprise mitosomes and hydrogenosomes, with the former having lost any role in energy metabolism along with the organelle genome. The mitosomes of the intestinal pathogen Giardia lamblia are the most highly reduced MROs known and have proven difficult to investigate because of their extreme divergence and their unique biophysical properties. Here, we implemented a novel strategy aimed at systematic analysis of the organelle proteome by iterative expansion of a protein-protein interaction network. We combined serial forward and reverse co-immunoprecipitations with mass spectrometry analysis, data mining, and validation by subcellular localization and/or functional analysis to generate an interactome network centered on a giardial Tom40 homolog. This iterative ab initio proteome reconstruction provided protein-protein interaction data in addition to identifying novel organelle proteins and functions. Building on this data we generated information on organelle replication, mitosome morphogenesis and organelle dynamics in living cells.

Genotyping and Descriptive Proteomics of a Potential Zoonotic Canine Strain of Giardia duodenalis, Infective to Mice

The zoonotic potential of giardiasis, as proposed by WHO since the late 70's, has been largely confirmed in this century. The genetic assemblages A and B of Giardia duodenalis are frequently isolated from human and canine hosts. Most of the assemblage A strains are not infective to adult mice, which can limit the range of studies regarding to biology of G. duodenalis, including virulence factors and the interaction with host immune system. This study aimed to determine the infectivity in mice of an assemblage A Giardia duodenalis strain (BHFC1) isolated from a dog and to classify the strain in sub-assemblages (AI, AII, AIII) through the phylogenetic analysis of beta-giardin (bg), triose phosphate isomerase (tpi) and glutamate dehydrogenase (gdh) genes. In addition, the proteomic profile of soluble and insoluble protein fractions of trophozoites was analyzed by 2D-electrophoresis. Accordingly, trophozoites of BHFC1 were highly infective to Swiss mice. The phylogenetic analysis of tpi and gdh revealed that BHFC1 clustered to sub-assemblage AI. The proteomic map of soluble and insoluble protein fractions led to the identification of 187 proteins of G. duodenalis, 27 of them corresponding to hypothetical proteins. Considering both soluble and soluble fractions, the vast majority of the identified proteins (n = 82) were classified as metabolic proteins, mainly associated with carbon and lipid metabolism, including 53 proteins with catalytic activity. Some of the identified proteins correspond to antigens while others can be correlated with virulence. Besides a significant complementation to the proteomic data of G. duodenalis, these data provide an important source of information for future studies on various aspects of the biology of this parasite, such as virulence factors and host and pathogen interactions.

Resolving the homology-function relationship through comparative genomics of membrane-trafficking machinery and parasite cell biology

With advances in DNA sequencing technology, it is increasingly common and tractable to informatically look for genes of interest in the genomic databases of parasitic organisms and infer cellular states. Assignment of a putative gene function based on homology to functionally characterized genes in other organisms, though powerful, relies on the implicit assumption of functional homology, i.e. that orthology indicates conserved function. Eukaryotes reveal a dazzling array of cellular features and structural organization, suggesting a concomitant diversity in their underlying molecular machinery. Significantly, examples of novel functions for pre-existing or new paralogues are not uncommon. Do these examples undermine the basic assumption of functional homology, especially in parasitic protists, which are often highly derived? Here we examine the extent to which functional homology exists between organisms spanning the eukaryotic lineage. By comparing membrane trafficking proteins between parasitic protists and traditional model organisms, where direct functional evidence is available, we find that function is indeed largely conserved between orthologues, albeit with significant adaptation arising from the unique biological features within each lineage.

An up-date on Giardia and giardiasis

Giardia intestinalis is a non-invasive protozoan parasite infecting the upper small intestine causing acute, watery diarrhea or giardiasis in 280 million people annually. Asymptomatic infections are equally common and recent data have suggested that infections even can be protective against other diarrheal diseases. Most symptomatic infections resolve spontaneously but infections can lead to chronic disease and treatment failures are becoming more common world-wide. Giardia infections can also result in irritable bowel syndrome (IBS) and food allergies after resolution. Until recently not much was known about the mechanism of giardiasis or the cause of post-giardiasis syndromes and treatment failures, but here we will describe the recent progress in these areas.

Induction of virulence factors in Giardia duodenalis independent of host attachment

Giardia duodenalis is responsible for the majority of parasitic gastroenteritis in humans worldwide. Host-parasite interaction models in vitro provide insights into disease and virulence and help us to understand pathogenesis. Using HT-29 intestinal epithelial cells (IEC) as a model we have demonstrated that initial sensitisation by host secretions reduces proclivity for trophozoite attachment, while inducing virulence factors. Host soluble factors triggered up-regulation of membrane and secreted proteins, including Tenascins, Cathepsin-B precursor, cystatin, and numerous Variant-specific Surface Proteins (VSPs). By comparison, host-cell attached trophozoites up-regulated intracellular pathways for ubiquitination, reactive oxygen species (ROS) detoxification and production of pyridoxal phosphate (PLP). We reason that these results demonstrate early pathogenesis in Giardia involves two independent host-parasite interactions. Motile trophozoites respond to soluble secreted signals, which deter attachment and induce expression of virulence factors. Trophozoites attached to host cells, in contrast, respond by up-regulating intracellular pathways involved in clearance of ROS, thus anticipating the host defence response.

Sensing parasites: Proteomic and advanced bio-detection alternatives

Parasitic diseases have a great impact in human and animal health. The gold standard for the diagnosis of the majority of parasitic infections is still conventional microscopy, which presents important limitations in terms of sensitivity and specificity and commonly requires highly trained technicians. More accurate molecular-based diagnostic tools are needed for the implementation of early detection, effective treatments and massive screenings with high-throughput capacities. In this respect, sensitive and affordable devices could greatly impact on sustainable control programmes which exist against parasitic diseases, especially in low income settings. Proteomics and nanotechnology approaches are valuable tools for sensing pathogens and host alteration signatures within microfluidic detection platforms. These new devices might provide novel solutions to fight parasitic diseases. Newly described specific parasite derived products with immune-modulatory properties have been postulated as the best candidates for the early and accurate detection of parasitic infections as well as for the blockage of parasite development. This review provides the most recent methodological and technological advances with great potential for bio-sensing parasites in their hosts, showing the newest opportunities offered by modern "-omics" and platforms for parasite detection and control.

The invasive potential of Giardia intestinalis in an in vivo model

Giardiasis is a neglected parasitic disease that affects primarily children, in whom it delays physical and mental development. The pathophysiology of giardiasis in not well understood, and most reports have identified Giardia intestinalis trophozoites only in the lumen and on the brush border of the small intestine. We identified Giardia trophozoites within the epithelium of the small intestine of a lactose intolerance patient. The Giardia trophozoites were obtained and cultured in vitro. In addition, we demonstrated Giardia trophozoite invasion in an animal model. Giardia trophozoites invaded the intestinal mucosa and submucosa of infected gerbils. The invasive trophozoites were observed at 21, 30 and 60 days age, and the average numbers of invaded sites were 17 ± 5, 15 ± 4, and 9 ± 3, respectively. We found trophozoites between epithelial cells, at the base of empty goblet cells, in lacteal vessels and within the submucosa. The morphological integrity of the invasive trophozoites was demonstrated via electron microscopy. The analysis of the gerbils infected with the trophozoites of the WB reference strain did not show intraepithelial trophozoites. These results demonstrate another Giardia pathogenic mechanism, opening the door to numerous future studies.

Probing the Biology of Giardia intestinalis Mitosomes Using In Vivo Enzymatic Tagging

Giardia intestinalis parasites contain mitosomes, one of the simplest mitochondrion-related organelles. Strategies to identify the functions of mitosomes have been limited mainly to homology detection, which is not suitable for identifying species-specific proteins and their functions. An in vivo enzymatic tagging technique based on the Escherichia coli biotin ligase (BirA) has been introduced to G. intestinalis; this method allows for the compartment-specific biotinylation of a protein of interest. Known proteins involved in the mitosomal protein import were in vivo tagged, cross-linked, and used to copurify complexes from the outer and inner mitosomal membranes in a single step. New proteins were then identified by mass spectrometry. This approach enabled the identification of highly diverged mitosomal Tim44 (GiTim44), the first known component of the mitosomal inner membrane translocase (TIM). In addition, our subsequent bioinformatics searches returned novel diverged Tim44 paralogs, which mediate the translation and mitosomal insertion of mitochondrially encoded proteins in other eukaryotes. However, most of the identified proteins are specific to G. intestinalis and even absent from the related diplomonad parasite Spironucleus salmonicida, thus reflecting the unique character of the mitosomal metabolism. The in vivo enzymatic tagging also showed that proteins enter the mitosome posttranslationally in an unfolded state and without vesicular transport.

Advances in understanding Giardia: determinants and mechanisms of chronic sequelae

Giardia lamblia is a flagellated protozoan that is the most common cause of intestinal parasitic infection in children living in resource-limited settings. The pathogenicity of Giardia has been debated since the parasite was first identified, and clinical outcomes vary across studies. Among recent perplexing findings are diametrically opposed associations between Giardia and acute versus persistent diarrhea and a poorly understood potential for long-term sequelae, including impaired child growth and cognitive development. The mechanisms driving these protean clinical outcomes remain elusive, but recent advances suggest that variability in Giardia strains, host nutritional status, the composition of microbiota, co-infecting enteropathogens, host genetically determined mucosal immune responses, and immune modulation by Giardia are all relevant factors influencing disease manifestations after Giardia infection.

Extracellular vesicles in parasitic diseases

Parasitic diseases affect billions of people and are considered a major public health issue. Close to 400 species are estimated to parasitize humans, of which around 90 are responsible for great clinical burden and mortality rates. Unfortunately, they are largely neglected as they are mainly endemic to poor regions. Of relevance to this review, there is accumulating evidence of the release of extracellular vesicles (EVs) in parasitic diseases, acting both in parasite–parasite inter-communication as well as in parasite–host interactions. EVs participate in the dissemination of the pathogen and play a role in the regulation of the host immune systems. Production of EVs from parasites or parasitized cells has been described for a number of parasitic infections. In this review, we provide the most relevant findings of the involvement of EVs in intercellular communication, modulation of immune responses, involvement in pathology, and their potential as new diagnostic tools and therapeutic agents in some of the major human parasitic pathogens.