Giardia lamblia: the roles of bile, lactic acid, and pH in the completion of the life cycle in vitro

Assessment of Drug Activities against Giardia Using Hyperspectral Raman Microscopy

This study demonstrates the capability of Raman microscopy for detecting structural differences in Giardia cells exposed to different drugs and incubation times. While metronidazole (MTZ) visibly affects the cells by inducing extracellular vesicle releases of toxic iron intermediates and modified triple-bond moieties, oseltamivir (OSM) alters the phenylalanine and lipid structures. Modifications in the heme protein environment and the transformation of iron from ferric to ferrous observed for both drug treatments are more notable for MTZ. Different contents and amounts of vesicle excretion are detected for 24 h or 48 h with MTZ incubation. At a shorter drug exposure, releases of altered proteins, glycogen, and phospholipids dominate. Agglomerates of transformed iron complexes from heme proteins and multiple-bond moieties prevail at 48 h of treatment. No such vesicle releases are present in the case of OSM usage. Drug incorporations into the cells and their impact on the plasma membrane and the dynamics of lipid raft confirmed by confocal fluorescence microscopy reveal a more destructive extent by OSM, corroborating the Raman results. Raman microscopy provides a broader understanding of the multifaceted factors and mechanisms responsible for giardiasis treatment or drug resistance by enabling a label-free, simultaneous monitoring of structural changes at the cellular and molecular levels.

Encystation stimuli sensing is mediated by adenylate cyclase AC2-dependent cAMP signaling in Giardia

Protozoan parasites use cAMP signaling to precisely regulate the place and time of developmental differentiation, yet it is unclear how this signaling is initiated. Encystation of the intestinal parasite Giardia lamblia can be activated by multiple stimuli, which we hypothesize result in a common physiological change. We demonstrate that bile alters plasma membrane fluidity by reducing cholesterol-rich lipid microdomains, while alkaline pH enhances bile function. Through depletion of the cAMP producing enzyme Adenylate Cyclase 2 (AC2) and the use of a newly developed Giardia-specific cAMP sensor, we show that AC2 is necessary for encystation stimuli-induced cAMP upregulation and activation of downstream signaling. Conversely, over expression of AC2 or exogenous cAMP were sufficient to initiate encystation. Our findings indicate that encystation stimuli induce membrane reorganization, trigger AC2-dependent cAMP upregulation, and initiate encystation-specific gene expression, thereby advancing our understanding of a critical stage in the life cycle of a globally important parasite.

A myeloid leukemia factor homolog is involved in tolerance to stresses and stress-induced protein metabolism in Giardia lamblia

BACKGROUND

The eukaryotic membrane vesicles contain specific sets of proteins that determine vesicle function and shuttle with specific destination. Giardia lamblia contains unknown cytosolic vesicles that are related to the identification of a homolog of human myeloid leukemia factor (MLF) named MLF vesicles (MLFVs). Previous studies suggest that MLF also colocalized with two autophagy machineries, FYVE and ATG8-like protein, and that MLFVs are stress-induced compartments for substrates of the proteasome or autophagy in response to rapamycin, MG132, and chloroquine treatment. A mutant protein of cyclin-dependent kinase 2, CDK2m3, was used to understand whether the aberrant proteins are targeted to degradative compratments. Interestingly, MLF was upregulated by CDK2m3 and they both colocalized within the same vesicles. Autophagy is a self-digestion process that is activated to remove damaged proteins for preventing cell death in response to various stresses. Because of the absence of some autophagy machineries, the mechanism of autophagy is unclear in G. lamblia.

RESULTS

In this study, we tested the six autophagosome and stress inducers in mammalian cells, including MG132, rapamycin, chloroquine, nocodazole, DTT, and G418, and found that their treatment increased reactive oxygen species production and vesicle number and level of MLF, FYVE, and ATG8-like protein in G. lamblia. Five stress inducers also increased the CDK2m3 protein levels and vesicles. Using stress inducers and knockdown system for MLF, we identified that stress induction of CDK2m3 was positively regulated by MLF. An autophagosome-reducing agent, 3-methyl adenine, can reduce MLF and CDK2m3 vesicles and proteins. In addition, knockdown of MLF with CRISPR/Cas9 system reduced cell survival upon treatment with stress inducers. Our newly developed complementation system for CRISPR/Cas9 indicated that complementation of MLF restored cell survival in response to stress inducers. Furthermore, human MLF2, like Giardia MLF, can increase cyst wall protein expression and cyst formation in G. lamblia, and it can colocalize with MLFVs and interact with MLF.

CONCLUSIONS

Our results suggest that MLF family proteins are functionally conserved in evolution. Our results also suggest an important role of MLF in survival in stress conditions and that MLFVs share similar stress-induced characteristics with autophagy compartments.

Encystation stimuli sensing mediated by adenylate cyclase AC2-dependent cAMP signaling in Giardia

Protozoan parasites use cAMP signaling to precisely regulate the place and time of developmental differentiation, yet it is unclear how this signaling is initiated. Encystation of the intestinal parasite Giardia lamblia can be activated by multiple stimuli, which we hypothesize result in a common physiological change. We demonstrate that bile alters plasma membrane fluidity by reducing cholesterol-rich lipid microdomains, while alkaline pH enhances bile function. Through depletion of the cAMP producing enzyme Adenylate Cyclase 2 (AC2) and the use of a newly developed Giardia-specific cAMP sensor, we show that AC2 is necessary for encystation stimuli-induced cAMP upregulation and activation of downstream signaling. Conversely, over expression of AC2 or exogenous cAMP were sufficient to initiate encystation. Our findings indicate that encystation stimuli induce membrane reorganization, trigger AC2-dependent cAMP upregulation, and initiate encystation-specific gene expression, thereby advancing our understanding of a critical stage in the life cycle of a globally important parasite.

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.

Giardial lipid rafts share virulence factors with secreted vesicles and participate in parasitic infection in mice

Giardia lamblia, a protozoan parasite, is a major cause of waterborne infection, worldwide. While the trophozoite form of this parasite induces pathological symptoms in the gut, the cyst form transmits the infection. Since Giardia is a noninvasive parasite, the actual mechanism by which it causes disease remains elusive. We have previously reported that Giardia assembles cholesterol and GM1 glycosphingolipid-enriched lipid rafts (LRs) that participate in encystation and cyst production. To further delineate the role of LRs in pathogenesis, we isolated LRs from Giardia and subjected them to proteomic analysis. Various cellular proteins including potential virulence factors-e.g., giardins, variant surface proteins, arginine deaminases, elongation factors, ornithine carbomyltransferases, and high cysteine-rich membrane proteins-were found to be present in LRs. Since Giardia secretes virulence factors encapsulated in extracellular vesicles (EVs) that induce proinflammatory responses in hosts, EVs released by the parasite were isolated and subjected to nanoparticle tracking and proteomic analysis. Two types of EV-i.e., small vesicles (SVs; <100 nm, exosome-like particles) and large vesicles (LVs; 100-400 nm, microvesicle-like particles)-were identified and found to contain a diverse group of proteins including above potential virulence factors. Although pretreatment of the parasite with two giardial lipid raft (gLR) disruptors, nystatin (27 μM) and oseltamivir (20 μM), altered the expression profiles of virulence factors in LVs and SVs, the effects were more robust in the case of SVs. To examine the potential role of rafts and vesicles in pathogenicity, Giardia-infected mice were treated with oseltamivir (1.5 and 3.0 mg/kg), and the shedding of cysts were monitored. We observed that this drug significantly reduced the parasite load in mice. Taken together, our results suggest that virulence factors partitioning in gLRs, released into the extracellular milieu via SVs and LVs, participate in spread of giardiasis and could be targeted for future drug development.

A cell-cycle-dependent GARP-like transcriptional repressor regulates the initiation of differentiation in Giardia lamblia

Transcriptional regulation of differentiation is critical for parasitic pathogens to adapt to environmental changes and regulate transmission. In response to encystation stimuli, Giardia lamblia shifts the distribution of the cell cycle toward G2 and induces the expression of cyst wall proteins (CWPs) within 2 to 4 h, indicating that key regulatory steps occur within the first 4 h of encystation. However, the role of transcription factors (TFs) in encystation has primarily been investigated at later time points. How TFs initiate encystation and link it to the cell cycle remains enigmatic. Here, we systematically screened six putative early up-regulated TFs for nuclear localization, established their dynamic expression profiles, and determined their functional role in regulating encystation. We found a critical repressor, Golden2, ARR-B, Psr-1–like protein 1 (GARP)–like protein 4 (GLP4), that increases rapidly after 30 min of encystation stimuli and down-regulates encystation-specific markers, including CWPs and enzymes in the cyst N-acetylgalactosamine pathway. Depletion of GLP4 increases cyst production. Importantly, we observe that G2+M cells exhibit higher levels of CWP1, resulting from the activation of myeloblastosis domain protein 2 (MYB2), a TF previously linked to encystation in Giardia. GLP4 up-regulation occurs in G1+S cells, suggesting a role in repressing MYB2 and encystation-specific genes in the G1+S phase of the cell cycle. Furthermore, we demonstrate that depletion of GLP4 up-regulates MYB2 and promotes encystation while overexpression of GLP4 down-regulates MYB2 and represses encystation. Together, these results suggest that Giardia employs a dose-dependent transcriptional response that involves the cell-cycle–regulated repressor GLP4 to orchestrate MYB2 and entry into the encystation pathway.

A Novel Spo11 Homologue Functions as a Positive Regulator in Cyst Differentiation in Giardia lamblia

Giardia lamblia persists in a dormant state with a protective cyst wall for transmission. It is incompletely known how three cyst wall proteins (CWPs) are coordinately synthesized during encystation. Meiotic recombination is required for sexual reproduction in animals, fungi, and plants. It is initiated by formation of double-stranded breaks by a topoisomerase-like Spo11. It has been shown that exchange of genetic material in the fused nuclei occurs during Giardia encystation, suggesting parasexual recombination processes of this protozoan. Giardia possesses an evolutionarily conserved Spo11 with typical domains for cleavage reaction and an upregulated expression pattern during encystation. In this study, we asked whether Spo11 can activate encystation process, like other topoisomerases we previously characterized. We found that Spo11 was capable of binding to both single-stranded and double-stranded DNA in vitro and that it could also bind to the cwp promoters in vivo as accessed in chromatin immunoprecipitation assays. Spo11 interacted with WRKY and MYB2 (named from myeloblastosis), transcription factors that can activate cwp gene expression during encystation. Interestingly, overexpression of Spo11 resulted in increased expression of cwp1-3 and myb2 genes and cyst formation. Mutation of the Tyr residue for the active site or two conserved residues corresponding to key DNA-binding residues for Arabidopsis Spo11 reduced the levels of cwp1-3 and myb2 gene expression and cyst formation. Targeted disruption of spo11 gene with CRISPR/Cas9 system led to a significant decrease in cwp1-3 and myb2 gene expression and cyst number. Our results suggest that Spo11 acts as a positive regulator for Giardia differentiation into cyst.

Giardia lamblia: Laboratory Maintenance, Lifecycle Induction, and Infection of Murine Models

Giardia lamblia is a protozoan parasite that is found ubiquitously throughout the world and is a major contributor to diarrheal disease. Giardia exhibits a biphasic lifestyle existing as either a dormant cyst or a vegetative trophozoite. Infections are typically initiated through the consumption of cyst-contaminated water or food. Giardia was first axenized in the 1970s and can be readily maintained in a laboratory setting. Additionally, Giardia is one of the few protozoans that can be induced to complete its complete lifecycle using laboratory methods. In this article, we outline protocols to maintain Giardia and induce passage through its lifecycle. We also provide protocols for infecting and quantifying parasites in an animal infection model. © 2020 Wiley Periodicals LLC. Basic Protocol 1: In vitro maintenance and growth of Giardia trophozoites Basic Protocol 2: In vitro encystation of Giardia cysts Basic Protocol 3: In vivo infections using Giardia trophozoites.

A myeloid leukemia factor homolog involved in encystation-induced protein metabolism in Giardia lamblia

BACKGROUND

Giardia lamblia differentiates into resistant cysts as an established model for dormancy. Myeloid leukemia factor (MLF) proteins are important regulators of cell differentiation. Giardia possesses a MLF homolog which was up-regulated during encystation and localized to unknown cytosolic vesicles named MLF vesicles (MLFVs).

METHODS

We used double staining for visualization of potential factors with role in protein metabolism pathway and a strategy that employed a deletion mutant, CDK2m3, to test the protein degradation pathway. We also explored whether autophagy or proteasomal degradation are regulators of Giardia encystation by treatment with MG132, rapamycin, or chloroquine.

RESULTS

Double staining of MLF and ISCU or CWP1 revealed no overlap between their vesicles. The aberrant CDK2m3 colocalized with MLFVs and formed complexes with MLF. MG132 increased the number of CDK2m3-localized vesicles and its protein level. We further found that MLF colocalized and interacted with a FYVE protein and an ATG8-like (ATG8L) protein, which were up-regulated during encystation and their expression induced Giardia encystation. The addition of MG132, rapamycin, or chloroquine, increased their levels and the number of their vesicles, and inhibited the cyst formation. MLF and FYVE were detected in exosomes released from culture.

CONCLUSIONS

The MLFVs are not mitosomes or encystation-specific vesicles, but are related with degradative pathway for CDK2m3. MLF, FYVE, and ATG8L play a positive role in encystation and function in protein clearance pathway, which is important for encystation and coordinated with Exosomes.

GENERAL SIGNIFICANCE

MLF, FYVE, and ATG8L may be involved an encystation-induced protein metabolism during Giardia differentiation.

A Novel Multiprotein Bridging Factor 1-Like Protein Induces Cyst Wall Protein Gene Expression and Cyst Differentiation in Giardia lamblia

The capacity to synthesize a protective cyst wall is critical for infectivity of Giardia lamblia. It is of interest to know the mechanism of coordinated synthesis of three cyst wall proteins (CWPs) during encystation, a differentiation process. Multiprotein bridging factor 1 (MBF1) gene family is a group of transcription coactivators that bridge various transcription factors. They are involved in cell growth and differentiation in yeast and animals, or in stress response in fungi and plants. We asked whether Giardia has MBF1-like genes and whether their products influence gene expression. BLAST searches of the Giardia genome database identified one gene encoding a putative MBF1 protein with a helix-turn-helix domain. We found that it can specifically bind to the AT-rich initiator promoters of the encystation-induced cwp1-3 and myb2 genes. MBF1 localized to cell nuclei and cytoplasm with higher expression during encystation. In addition, overexpression of MBF1 induced cwp1-3 and myb2 gene expression and cyst generation. Mutation of the helixes in the helix-turn-helix domain reduced cwp1-3 and myb2 gene expression and cyst generation. Chromatin immunoprecipitation assays confirmed the binding of MBF1 to the promoters with its binding sites in vivo. We also found that MBF1 can interact with E2F1, Pax2, WRKY, and Myb2 transcription factors that coordinately up-regulate the cwp genes during encystation. Using a CRISPR/Cas9 system for targeted disruption of mbf1 gene, we found a downregulation of cwp1-3 and myb2 genes and decrease of cyst generation. Our results suggest that MBF1 is functionally conserved and positively regulates Giardia cyst differentiation.

High-Yield Purification of Giardia intestinalis Cysts from Fecal Samples

Giardia is an enteric protozoan parasite that causes gastroenteritis in all classes of vertebrates. It is ranked among the leading causes of death in children under 5 years of age. Giardiasis affects approximately 280 million people worldwide annually, a situation exacerbated by the low availability of effective treatments and the lack of a vaccine. In addition, the parasite is difficult to manipulate in in vitro environments, which hampers the development of effective disease management strategies. This article highlights the development of a method for the purification of viable Giardia cysts from fecal samples, verified by a trypan blue dye exclusion test. This protocol produces a 10-fold increase in yield over current methods. By combining sucrose flotation with gated filtration, the protocol significantly reduces the amount of debris in the purified cysts suspension. Cyst viability is verified by a trypan blue dye exclusion test. The ability to purify large quantities of Giardia from fecal samples could advance the development of effective treatments to target this worldwide prevalent parasite. © 2020 Wiley Periodicals LLC. Basic Protocol: Purification of Giardia cysts from fecal samples Support Protocol: Cyst viability test.

Triazoxins: Novel nucleosides with anti-Giardia activity

Novel nucleoside analogues named "triazoxins" were synthesized. Of these, two analogues were found to be highly effective against Giardia lamblia, an intestinal parasite and a major cause of waterborne infection, worldwide. While compound 7 reduced the growth of trophozoites in culture (IC50, ~5 μM), compound 21 blocked the in vitro cyst production (IC50 ~5 μM). Compound 21 was also effective against trophozoites (IC50, ~36 μM). A third analogue (compound 8) was effective against both trophozoites (IC50, ~36 μM) and cysts (IC50, ~20 μM) although at higher concentration. Thus triazoxin analogues are unique and exhibit morphology (i.e., trohozoites or cysts) -specific effects against Giardia.

DNA topoisomerase IIIβ promotes cyst generation by inducing cyst wall protein gene expression in Giardia lamblia

Giardia lamblia causes waterborne diarrhoea by transmission of infective cysts. Three cyst wall proteins are highly expressed in a concerted manner during encystation of trophozoites into cysts. However, their gene regulatory mechanism is still largely unknown. DNA topoisomerases control topological homeostasis of genomic DNA during replication, transcription and chromosome segregation. They are involved in a variety of cellular processes including cell cycle, cell proliferation and differentiation, so they may be valuable drug targets. Giardia lamblia possesses a type IA DNA topoisomerase (TOP3β) with similarity to the mammalian topoisomerase IIIβ. We found that TOP3β was upregulated during encystation and it possessed DNA-binding and cleavage activity. TOP3β can bind to the cwp promoters in vivo using norfloxacin-mediated topoisomerase immunoprecipitation assays. We also found TOP3β can interact with MYB2, a transcription factor involved in the coordinate expression of cwp1-3 genes during encystation. Interestingly, overexpression of TOP3β increased expression of cwp1-3 and myb2 genes and cyst formation. Microarray analysis confirmed upregulation of cwp1-3 and myb2 genes by TOP3β. Mutation of the catalytically important Tyr residue, deletion of C-terminal zinc ribbon domain or further deletion of partial catalytic core domain reduced the levels of cleavage activity, cwp1-3 and myb2 gene expression, and cyst formation. Interestingly, some of these mutant proteins were mis-localized to cytoplasm. Using a CRISPR/Cas9 system for targeted disruption of top3β gene, we found a significant decrease in cwp1-3 and myb2 gene expression and cyst number. Our results suggest that TOP3β may be functionally conserved, and involved in inducing Giardia cyst formation.

A Targeted Mass Spectrometric Analysis Reveals the Presence of a Reduced but Dynamic Sphingolipid Metabolic Pathway in an Ancient Protozoan, Giardia lamblia

Giardia lamblia, a single-celled eukaryote, colonizes and thrives in the small intestine of humans. Because of its compact and reduced genome, Giardia has adapted a “minimalistic” life style, as it becomes dependent on available resources of the small intestine. Because Giardia expresses fewer sphingolipid (SL) genes—and glycosphingolipids are critical for encystation—we investigated the SL metabolic cycle in this parasite. A tandem mass spectrometry (MS/MS) analysis reveals that major SLs in Giardia include sphingomyelins, sphingoid bases, ceramides, and glycosylceramides. Many of these lipids are obtained by Giardia from the growth medium, remodeled at their fatty acyl chains and end up in the spent medium. For instance, ceramide-1-phosphate, a proinflammatory molecule that is not present in the culture medium, is generated from sphingosine (abundant in the culture medium) possibly by remodeling reactions. It is then subsequently released into the spent medium. Thus, the secretion of ceramide-1-phospate and other SL derivatives by Giardia could be associated with inflammatory bowel disease observed in acute giardiasis. Additionally, we found that the levels of SLs increase in encysting Giardia and are differentially regulated throughout the encystation cycle. We propose that SL metabolism is important for this parasite and, could serve as potential targets for developing novel anti-giardial agents.

Lactoferrin and lactoferricin endocytosis halt Giardia cell growth and prevent infective cyst production

Lactoferrin (LF) is an 80 KDa iron-binding glycoprotein that plays a significant role in the innate immune system and is considered to be an important microbicide molecule. It has been suggested to be effective in the treatment of giardiasis, an intestinal disease caused by the protozoan parasite G. lamblia. However, the molecular mechanisms by which LF exerts its effect on this parasite are unknown. Most of the microbicidal activity of human or bovine LF (hLF or bLF) has been associated with the N-terminal region of the mature LF - lactoferricin (LFcin). LFcin is produced by pepsin cleavage of the native protein in vitro and likely in vivo. In this work, we analyse the participation of the endocytic machinery of G. lamblia in the internalization of bLF and bLFcin and their effects on cell homeostasis. Our results show that, when bLF or bLFcin are internalized by receptor-mediated endocytosis, cell growth stops, and morphological changes are produced in the trophozoites, which ultimately will produce immature cysts. Our findings contribute to disclose the fine mechanism by which bLF and bLFcin may function as an antigiardial molecule and why they have therapeutic potential to eradicate giardiasis.

A review of the traditional use of southern African medicinal plants for the treatment of selected parasite infections affecting humans

ETHNOPHARMACOLOGICAL RELEVANCE

Worldwide, more than three billion cases of parasitic disease are reported yearly and it is likely that this figure is substantially under-estimated. Approximately one in six people globally are estimated to be infected with at least one parasite species annually. In South Africa, the prevalence of Schistosoma haematobium (bilharzia) and intestinal worms and helminths are particularly high, especially in children and in crowded or poorer rural communities with inadequate sanitation and nutrition. Despite alarmingly high estimates, medical research into parasitic diseases remains neglected and only malaria receives significant attention and funding. Traditional medicines have been used for centuries in Africa by multiple ethnic groups and many people rely on these healing systems as their primary healthcare modality. The traditional use of South African medicinal plants to treat parasite infestations is relatively well documented, and it is important to link these traditional uses to scientific evidence validating efficacy.

AIM OF THE STUDY

To document the medicinal plants used for parasitic infections and critically review the literature on the anti-parasitic properties of South African plants against some neglected parasitic diseases.

MATERIALS AND METHODS

A review of the literature (ethnobotanical books and publications documenting traditional plant use) was undertaken related to specific medicinal use for parasitic infections in Southern Africa. Inclusion criteria focused on human use. Exclusion criteria included veterinary use and malaria due to the extensive nature of these subject matters. An in-depth analysis of previous studies was undertaken and future prospectives are considered.

RESULTS

In particular, bilharzia, gastrointestinal worms and helminths, ectoparasites, trichomoniasis, leishmaniasis and trypanosomiasis are reviewed with special emphasis on the gaps in research.

CONCLUSIONS

Despite the availability of relatively extensive ethnobotanical records on the anti-parasitic properties of southern African medicinal plants, the antiparasitic properties of many plants have been poorly examined. There was in many instances a lack of evidence to support traditional use of many species towards some parasites and research is urgently needed in this area.

Morphological and physiological characteristics of a virulent and zoonotic assemblage A Giardia duodenalis canine strain

Giardiasis is an intestinal parasitosis that affects millions of people worldwide and is considered a zoonotic disease. Frequently in contact with humans, dogs are the main host involved in this zoonotic transmission. Here, we compared some aspects of Giardia duodenalis biology between two strains: a recently isolated dog strain (BHFC1) and a human reference strain (Portland-1). Growth curve analysis revealed that BHFC1 trophozoites multiply faster than the human isolate Portland-1 in axenic culture, but has a lower rate of cysts formation. Scanning electron microscopy revealed that BHFC1 trophozoites have the same conventional shape and morphological structures expected for G. duodenalis trophozoites, but presented a more prominent flange. For the best of our knowledge, this work is the first description of morphological aspects and encystation process of a G. duodenalis strain isolated from a dog. Since BHFC1 and Portland-1 have been maintained in axenic cultures for different periods of time, differences observed in growth, encystation rates and flange size may be attributed to adaptation of Portland-1 to axenic culture and lack of the environmental pressures. BHFC1 can be useful as tool for better understanding of Giardia duodenalis biology.

Giardia Colonizes and Encysts in High-Density Foci in the Murine Small Intestine

Giardia is a single-celled parasite causing significant diarrheal disease in several hundred million people worldwide. Due to limited access to the site of infection in the gastrointestinal tract, our understanding of the dynamics of Giardia infections in the host has remained limited and largely inferred from laboratory culture. To better understand Giardia physiology and colonization in the host, we developed imaging methods to quantify Giardia expressing bioluminescent physiological reporters in two relevant animal models. We discovered that parasites primarily colonize and encyst in the proximal small intestine in discrete, high-density foci. We also show that high parasite density contributes to encystation initiation.

Giardia lamblia is a highly prevalent yet understudied protistan parasite causing significant diarrheal disease worldwide. Hosts ingest Giardia cysts from contaminated sources. In the gastrointestinal tract, cysts excyst to become motile trophozoites, colonizing and attaching to the gut epithelium. Trophozoites later differentiate into infectious cysts that are excreted and contaminate the environment. Due to the limited accessibility of the gut, the temporospatial dynamics of giardiasis in the host are largely inferred from laboratory culture and thus may not mirror Giardia physiology in the host. Here, we have developed bioluminescent imaging (BLI) to directly interrogate and quantify the in vivo temporospatial dynamics of Giardia infection, thereby providing an improved murine model to evaluate anti-Giardia drugs. Using BLI, we determined that parasites primarily colonize the proximal small intestine nonuniformly in high-density foci. By imaging encystation-specific bioreporters, we show that encystation initiates shortly after inoculation and continues throughout the duration of infection. Encystation also initiates in high-density foci in the proximal small intestine, and high density contributes to the initiation of encystation in laboratory culture. We suggest that these high-density in vivo foci of colonizing and encysting Giardia likely result in localized disruption to the epithelium. This more accurate visualization of giardiasis redefines the dynamics of the in vivo Giardia life cycle, paving the way for future mechanistic studies of density-dependent parasitic processes in the host.

IMPORTANCEGiardia is a single-celled parasite causing significant diarrheal disease in several hundred million people worldwide. Due to limited access to the site of infection in the gastrointestinal tract, our understanding of the dynamics of Giardia infections in the host has remained limited and largely inferred from laboratory culture. To better understand Giardia physiology and colonization in the host, we developed imaging methods to quantify Giardia expressing bioluminescent physiological reporters in two relevant animal models. We discovered that parasites primarily colonize and encyst in the proximal small intestine in discrete, high-density foci. We also show that high parasite density contributes to encystation initiation.

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.

Glucosylceramide transferase in Giardia preferentially catalyzes the synthesis of galactosylceramide during encystation

The stage differentiation from trophozoite to cyst (i.e., encystation) is an essential step for Giardia to survive outside its human host and spread the infection via the fecal-oral route. We have previously shown that Giardia expresses glucosylceramide transferase 1 (GlcT1) enzyme, the activity of which is elevated during encystation. We have also reported that blocking the activity of gGlcT1 interferes with the biogenesis of encystation-specific vesicles (ESVs) and cyst viability in Giardia. To further understand the role of this enzyme and how it regulates encystation, we overexpressed, knocked down, and rescued the giardial GlcT1 (gGlcT1) gene and measured its enzymatic activity in live parasites as well as in isolated membrane fractions using NBD-ceramide and UDP-glucose or UDP-galactose. We observed that gGlcT1 is able to catalyze the synthesis of both glucosylceramide (GlcCer) and galactosylceramide (GalCer), however the synthesis of GalCer is 2-3 fold higher than of GlcCer. Although both activities follow Michaelis-Menten kinetics, the bindings of UDP-glucose and UDP-galactose with the enzyme appear to be non-competitive and independent of each other. The modulation of gGlcT1 synthesis concomitantly influenced the expression cyst-wall protein (CWP) and overall encystation. We propose that gGlcT1 is a unique enzyme and that Giardia uses this enzyme to synthesize both GlcCer and GalCer to facilitate the process of encystation/cyst production.

Specific histone modifications play critical roles in the control of encystation and antigenic variation in the early-branching eukaryote Giardia lamblia

During evolution, parasitic microorganisms have faced the challenges of adapting to different environments to colonize a variety of hosts. Giardia lamblia, a common cause of intestinal disease, has developed fascinating strategies to adapt both outside and inside its host's intestine, such as trophozoite differentiation into cyst and the switching of its major surface antigens. How gene expression is regulated during these adaptive processes remains undefined. Giardia lacks some typical eukaryotic features, like canonical transcription factors, linker histone H1, and complex promoter regions; suggesting that post-transcriptional and translational control of gene expression is essential for parasite survival. However, epigenetic factors may also play critical roles at the transcriptional level. Here, we describe the most common post-translational histone modifications; characterize enzymes involved in these reactions, and analyze their association with the Giardia's differentiation processes. We present evidence that NAD⁺-dependent and NAD⁺-independent histone deacetylases regulate encystation; however, a unique NAD⁺-independent histone deacetylase modulate antigenic switching. The rates of acetylation of H4K8 and H4K16 are critical for encystation, whereas a decrease in acetylation of H4K8 and methylation of H3K9 occur preferentially during antigenic variation. These results show the complexity of the mechanisms regulating gene expression in this minimalistic protozoan parasite.

Deconjugated Bile Salts Produced by Extracellular Bile-Salt Hydrolase-Like Activities from the Probiotic Lactobacillus johnsonii La1 Inhibit Giardia duodenalis In vitro Growth

Giardiasis, currently considered a neglected disease, is caused by the intestinal protozoan parasite Giardia duodenalis and is widely spread in human as well as domestic and wild animals. The lack of appropriate medications and the spread of resistant parasite strains urgently call for the development of novel therapeutic strategies. Host microbiota or certain probiotic strains have the capacity to provide some protection against giardiasis. By combining biological and biochemical approaches, we have been able to decipher a molecular mechanism used by the probiotic strain Lactobacillus johnsonii La1 to prevent Giardia growth in vitro. We provide evidence that the supernatant of this strain contains active principle(s) not directly toxic to Giardia but able to convert non-toxic components of bile into components highly toxic to Giardia. By using bile acid profiling, these components were identified as deconjugated bile-salts. A bacterial bile-salt-hydrolase of commercial origin was able to mimic the properties of the supernatant. Mass spectrometric analysis of the bacterial supernatant identified two of the three bile-salt-hydrolases encoded in the genome of this probiotic strain. These observations document a possible mechanism by which L. johnsonii La1, by secreting, or releasing BSH-like activity(ies) in the vicinity of replicating Giardia in an environment where bile is present and abundant, can fight this parasite. This discovery has both fundamental and applied outcomes to fight giardiasis, based on local delivery of deconjugated bile salts, enzyme deconjugation of bile components, or natural or recombinant probiotic strains that secrete or release such deconjugating activities in a compartment where both bile salts and Giardia are present.

Early-life enteric infections: relation between chronic systemic inflammation and poor cognition in children

The intestinal microbiota undergoes active remodeling in the first 6 to 18 months of life, during which time the characteristics of the adult microbiota are developed. This process is strongly influenced by the early diet and enteric pathogens. Enteric infections and malnutrition early in life may favor microbiota dysbiosis and small intestinal bacterial overgrowth, resulting in intestinal barrier dysfunction and translocation of intestinal bacterial products, ultimately leading to low-grade, chronic, subclinical systemic inflammation. The leaky gut-derived low-grade systemic inflammation may have profound consequences on the gut-liver-brain axis, compromising normal growth, metabolism, and cognitive development. This review examines recent data suggesting that early-life enteric infections that lead to intestinal barrier disruption may shift the intestinal microbiota toward chronic systemic inflammation and subsequent impaired cognitive development.

Sphingolipids, Lipid Rafts, and Giardial Encystation: The Show Must Go On

Sphingolipids are sphingosine-based phospholipids, which are present in the plasma and endomembranes of many eukaryotic cells. These lipids are involved in various cellular functions, including cell growth, differentiation, and apoptosis. In addition, sphingolipid and cholesterol-enriched membrane microdomains (also called "lipid rafts") contain a set of proteins and lipids, which take part in the signaling process in response to intra- or extracellular stimuli. Recent findings suggest that sphingolipids, especially glucosylceramide, play a critical role in inducing encystation and maintaining the cyst viability in Giardia. Similarly, the assembly/disassembly of lipid rafts modulates the encystation and cyst production of this ubiquitous enteric parasite. In this review article, we discuss the overall progress in the field and examine whether sphingolipids and lipid rafts can be used as novel targets for designing therapies to control infection by Giardia, which is rampant in developing countries, where children are especially vulnerable.

The assembly of GM1 glycolipid- and cholesterol-enriched raft-like membrane microdomains is important for giardial encystation

Although encystation (or cyst formation) is an important step of the life cycle of Giardia, the cellular events that trigger encystation are poorly understood. Because membrane microdomains are involved in inducing growth and differentiation in many eukaryotes, we wondered if these raft-like domains are assembled by this parasite and participate in the encystation process. Since the GM1 ganglioside is a major constituent of mammalian lipid rafts (LRs) and known to react with cholera toxin B (CTXB), we used Alexa Fluor-conjugated CTXB and GM1 antibodies to detect giardial LRs. Raft-like structures in trophozoites are located in the plasma membranes and on the periphery of ventral discs. In cysts, however, they are localized in the membranes beneath the cyst wall. Nystatin and filipin III, two cholesterol-binding agents, and oseltamivir (Tamiflu), a viral neuraminidase inhibitor, disassembled the microdomains, as evidenced by reduced staining of trophozoites with CTXB and GM1 antibodies. GM1- and cholesterol-enriched LRs were isolated from Giardia by density gradient centrifugation and found to be sensitive to nystatin and oseltamivir. The involvement of LRs in encystation could be supported by the observation that raft inhibitors interrupted the biogenesis of encystation-specific vesicles and cyst production. Furthermore, culturing of trophozoites in dialyzed medium containing fetal bovine serum (which is low in cholesterol) reduced raft assembly and encystation, which could be rescued by adding cholesterol from the outside. Our results suggest that Giardia is able to form GM1- and cholesterol-enriched lipid rafts and these raft domains are important for encystation.

Trans-spliced heat shock protein 90 modulates encystation in Giardia lamblia

Background

Hsp90 from Giardia lamblia is expressed by splicing of two independently transcribed RNA molecules, coded by genes named HspN and HspC located 777 kb apart. The reasons underlying such unique trans-splicing based generation of GlHsp90 remain unclear.

Principle Finding

In this study using mass-spectrometry we identify the sequence of the unique, junctional peptide contributed by the 5′ UTR of HspC ORF. This peptide is critical for the catalytic function of Hsp90 as it harbours an essential “Arg” in its sequence. We also show that full length GlHsp90 possesses all the functional hall marks of a canonical Hsp90 including its ability to bind and hydrolyze ATP. Using qRT-PCR as well as western blotting approach we find the reconstructed Hsp90 to be induced in response to heat shock. On the contrary we find GlHsp90 to be down regulated during transition from proliferative trophozoites to environmentally resistant cysts. This down regulation of GlHsp90 appears to be mechanistically linked to the encystation process as we find pharmacological inhibition of GlHsp90 function to specifically induce encystation.

Significance

Our results implicate the trans-spliced GlHsp90 from Giardia lamblia to regulate an essential stage transition in the life cycle of this important human parasite.

Giardia lamblia is one of the most common causes of diarrhoea across the globe. The disease can result in fatalities especially in small children. The parasite is transmitted by contaminated food through faeco-oral route due to unhygienic habits. The parasite exhibits two stages during its lifecycle; namely cysts and trophozoites. Due to their environmentally resistant hardy nature cysts are transmitted through contaminated food into the human body. Upon entry into the human body they convert into active trophozoites and cause pathogenesis of the disease. In the course of infection within the host, some of the trophozoites convert back into cysts and are released in the environment through the faeces. The mechanisms and signals that convert the parasite from trophozoites to cysts are not yet known. Our study, for the first time, implicates heat shock protein 90 of the parasite in the conversion of trophozoites into cysts in the intestine of the infected human body. Hsp90 is famous for its ability to sense environmental changes and provide cues for stage-switch in related parasites. In addition to providing a glimpse into molecular mechanisms of stage inter-conversion, our results suggest potential new ways of treating this important human infection.

The proteome landscape of Giardia lamblia encystation

Giardia lamblia is an intestinal protozoan parasite required to survive in the environment in order to be transmitted to a new host. To ensure parasite survival, flagellated trophozoites colonizing the small intestine differentiate into non-motile environmentally-resistant cysts which are then shed in the environment. This cell differentiation process called encystation is characterized by significant morphological remodeling which includes secretion of large amounts of cyst wall material. Although much is known about the transcriptional regulation of encystation and the synthesis and trafficking of cyst wall material, the investigation of global changes in protein content and abundance during G. lamblia encystation is still unaddressed.

In this study, we report on the quantitative analysis of the G. lamblia proteome during encystation using tandem mass spectrometry. Quantification of more than 1000 proteins revealed major changes in protein abundance in early, mid and late encystation, notably in constitutive secretory protein trafficking. Early stages of encystation were marked by a striking decrease of endoplasmic reticulum-targeted variant-specific surface proteins and significant increases in cytoskeleton regulatory components, NEK protein kinases and proteins involved in protein folding and glycolysis. This was in stark contrast to cells in the later stages of encystation which presented a surprisingly similar proteome composition to non-encysting trophozoites. Altogether these data constitute the first quantitative atlas of the Giardia proteome covering the whole process of encystation and point towards an important role for post-transcriptional control of gene expression in Giardia differentiation. Furthermore, our data provide a valuable resource for the community-based annotation effort of the G. lamblia genome, where almost 70% of all predicted gene models remains “hypothetical”.

Commitment to cyst formation in Giardia

Giardia trophozoites differentiate into infectious cysts (encystment) in response to physiological stimuli; encystment is crucial for Giardia's transmission, survival and pathogenesis. In vitro, Giardia encysts when bile sequesters lipids necessary for this lipid auxotroph, and in vivo they encyst to infect new hosts. In this study, we investigated, for the first time, commitment to encystment in Giardia using both molecular and cellular techniques. We show that after 3-6 h in inducing conditions, encysting trophozoites continue to encyst regardless of whether the inducing stimulus remains. We propose that a trophozoite's inability to revert to a growing or dividing trophozoite represents a commitment to encystment. The onset of commitment correlated with the appearance of encystment specific vesicles (ESVs) and encystment specific protein synthesis. These observations suggest the involvement of regulatory pathways with the ability to 'remember' a transient signal long after its removal; a property that enables encysting trophozoites to complete the encystment process should the unfavourable triggering condition(s) change. The ability to form cysts in response to transient signals or, as we have highlighted in this paper, the ability of a small percentage of the population to form cysts without an inducer is vital for the maintenance of infection within populations.

Non-invasive investigation of Spironucleus vortens transmission in freshwater angelfish Pterophyllum scalare

Spironucleus vortens is a protozoan fish parasite of veterinary and economic importance in the ornamental aquaculture industry. Despite this, key aspects of the life cycle of this organism, including its mode of transmission, have not been fully elucidated. We developed a non-invasive method for quantifying S. vortens in freshwater angelfish, which was then used to investigate parasite transmission and aggregation within host populations. As previously observed for S. meleagridis and S. salmonis, motile S. vortens trophozoites were detected in host faeces using light microscopy. Species-level identification of these flagellates was confirmed using 16S rDNA PCR. Faecal trophozoite counts were significantly correlated with trophozoite counts from the posterior intestine, the primary habitat of the parasite. This novel finding allowed effective prediction of intestinal parasite load from faecal counts. Overall, faecal count data revealed that 20% of hosts harbour 83% of parasites, conforming to the Pareto Principle (80/20 rule) of parasite aggregation with implications for parasite transmission. Trophozoites survived for ≥36 d outside the host within faeces and remained motile at low pH (comparable with that of angelfish stomach). No putative S. vortens cysts were observed in cultures or faecal samples. This calls into question the commonly accepted hypothesis that a protective cyst is required in the life cycle of S. vortens to facilitate transmission to a new host.

Glucosylceramide transferase activity is critical for encystation and viable cyst production by an intestinal protozoan, Giardia lamblia

The production of viable cysts by Giardia is essential for its survival in the environment and for spreading the infection via contaminated food and water. The hallmark of cyst production (also known as encystation) is the biogenesis of encystation-specific vesicles (ESVs) that transport cyst wall proteins to the plasma membrane of the trophozoite before laying down the protective cyst wall. However, the molecules that regulate ESV biogenesis and maintain cyst viability have never before been identified. Here, we report that giardial glucosylceramide transferase-1 (gGlcT1), an enzyme of sphingolipid biosynthesis, plays a key role in ESV biogenesis and maintaining cyst viability. We find that overexpression of this enzyme induced the formation of aggregated/enlarged ESVs and generated clustered cysts with reduced viability. The silencing of gGlcT1 synthesis by antisense morpholino oligonucleotide abolished ESV production and generated mostly nonviable cysts. Interestingly, when gGlcT1-overexpressed Giardia was transfected with anti-gGlcT1 morpholino, the enzyme activity, vesicle biogenesis, and cyst viability returned to normal, suggesting that the regulated expression of gGlcT1 is important for encystation and viable cyst production. Furthermore, the overexpression of gGlcT1 increased the influx of membrane lipids and fatty acids without altering the fluidity of plasma membranes, indicating that the expression of gGlcT1 activity is linked to lipid internalization and maintaining the overall lipid balance in this parasite. Taken together, our results suggest that gGlcT1 is a key player of ESV biogenesis and cyst viability and therefore could be targeted for developing new anti-giardial therapies.

Evaluation of drugs and stationary growth on the cell cycle of Giardia intestinalis

We examined the effect of aphidicolin, colchicine, demecolcine, fluorouracil, hydroxyurea, and nocodazole, as well as nutrient deprivation on the Giardia intestinalis cell cycle. Aphidicolin was the only drug that was able to block the cell cycle at a specific stage (G1/S), and permit cells to resume growth at a high rate upon its removal. Nutrient deprivation resulted in a portion of G2/M cells completing mitosis and cytokinesis in synchrony during the recovery period, but this synchrony was shortly lost and a sample containing a predominance of G1 cells could not be obtained. Flow cytometry analysis of normal and untreated Giardia cultures showed the occasional appearance of a small percentage of cells with a DNA content of 16C, which is twice the DNA content of G2 cells. However, this 16C peak is larger and more frequently observed in drug-treated Giardia. These 16C are likely produced from endoreplication of 8C/G2 cells, and we propose that they represent a pre-encystation stage that is induced by drug treatments and other stressors.

Nuclear inheritance and genetic exchange without meiosis in the binucleate parasite Giardia intestinalis

The protozoan parasite Giardia intestinalis (also known as Giardia lamblia) is a major waterborne pathogen. During its life cycle, Giardia alternates between the actively growing trophozoite, which has two diploid nuclei with low levels of allelic heterozygosity, and the infectious cyst, which has four nuclei and a tough outer wall. Although the formation of the cyst wall has been studied extensively, we still lack basic knowledge about many fundamental aspects of the cyst, including the sources of the four nuclei and their distribution during the transformation from cyst into trophozoite. In this study, we tracked the identities of the nuclei in the trophozoite and cyst using integrated nuclear markers and immunofluorescence staining. We demonstrate that the cyst is formed from a single trophozoite by a mitotic division without cytokinesis and not by the fusion of two trophozoites. During excystation, the cell completes cytokinesis to form two daughter trophozoites. The non-identical nuclear pairs derived from the parent trophozoite remain associated in the cyst and are distributed to daughter cells during excystation as pairs. Thus, nuclear sorting (such that each daughter cell receives a pair of identical nuclei) does not appear to be a mechanism by which Giardia reduces heterozygosity between its nuclei. Rather, we show that the cyst nuclei exchange chromosomal genetic material, perhaps as a way to reduce heterozygosity in the absence of meiosis and sex, which have not been described in Giardia. These results shed light on fundamental aspects of the Giardia life cycle and have implications for our understanding of the population genetics and cell biology of this binucleate parasite.

Glycogen storage and degradation during in vitro growth and differentiation of Giardia intestinalis

Giardia intestinalis is the causative agent of human giardiasis, a common diarrheal illness worldwide. Despite its global distribution and prevalence, many questions regarding its basic biology and metabolism remain unanswered. In this study, we examine the accumulation and degradation of glycogen, an important source of stored carbon and energy, during the in vitro growth and differentiation of G. intestinalis . We report that, as G. intestinalis progresses through its growth cycle, cultures of trophozoites accumulate glycogen during the lag and early logarithmic phases of growth and then utilize this compound during their remaining logarithmic growth. As cultures enter the stationary phase of growth, they re-accumulate glycogen stores. The activity of glycogen phosphorylase, an enzyme involved in glycogen metabolism, also varied throughout in vitro trophozoite growth. During the in vitro induction of trophozoite differentiation into water-resistant cyst forms, the cultures initially accumulated stores of glycogen which diminished throughout transition to the cyst form. This observation is suggestive of a role for glycogen in the differentiation process. These studies represent the first thorough analysis of changes in glycogen content and glycogen phosphorylase activity during G. intestinalis growth and differentiation.

In vitro lipolysis models as a tool for the characterization of oral lipid and surfactant based drug delivery systems

With the increasing interest in lipid and surfactant based drug delivery systems (LSBDDS) for oral delivery of poorly soluble drugs, the need for efficient development tools is emerging. In vitro lipolysis models, simulating the digestion in the small intestine, is a promising tool in this regard. Several different in vitro lipolysis models have been used for characterization of LSBDDS, all using porcine pancreatin as lipase source, and primarily differing in the addition scheme of calcium and the kind of bile acids employed. Both calcium and bile influence the lipolysis. Calcium have been used both as fixed addition at the beginning of the experiment and with a continuous addition during lipolysis. Both pure bile acids and crude porcine bile extract have been used. Lipolysis of LSBDDS will generate mixed micelles, as well as lamellar and hexagonal phases. These have been characterized by dynamic light scattering, cryogenic transmission electron microscopy and small angle X-ray scattering. The faith of drug during in vitro digestion of a LSBDDS is often studied by ultracentrifugation and quantification of drug in the different phases formed. Further, drug precipitated during in vitro lipolysis has been characterized by X-ray powder diffraction and polarized light microscopy.

The transcriptional response to encystation stimuli in Giardia lamblia is restricted to a small set of genes

The protozoan parasite Giardia lamblia undergoes stage differentiation in the small intestine of the host to an environmentally resistant and infectious cyst. Encystation involves the secretion of an extracellular matrix comprised of cyst wall proteins (CWPs) and a β(1-3)-GalNAc homopolymer. Upon the induction of encystation, genes coding for CWPs are switched on, and mRNAs coding for a Myb transcription factor and enzymes involved in cyst wall glycan synthesis are upregulated. Encystation in vitro is triggered by several protocols, which call for changes in bile concentrations or availability of lipids, and elevated pH. However, the conditions for induction are not standardized and we predicted significant protocol-specific side effects. This makes reliable identification of encystation factors difficult. Here, we exploited the possibility of inducing encystation with two different protocols, which we show to be equally effective, for a comparative mRNA profile analysis. The standard encystation protocol induced a bipartite transcriptional response with surprisingly minor involvement of stress genes. A comparative analysis revealed a core set of only 18 encystation genes and showed that a majority of genes was indeed upregulated as a side effect of inducing conditions. We also established a Myb binding sequence as a signature motif in encystation promoters, suggesting coordinated regulation of these factors.

Selective condensation drives partitioning and sequential secretion of cyst wall proteins in differentiating Giardia lamblia

Controlled secretion of a protective extracellular matrix is required for transmission of the infective stage of a large number of protozoan and metazoan parasites. Differentiating trophozoites of the highly minimized protozoan parasite Giardia lamblia secrete the proteinaceous portion of the cyst wall material (CWM) consisting of three paralogous cyst wall proteins (CWP1–3) via organelles termed encystation-specific vesicles (ESVs). Phylogenetic and molecular data indicate that Diplomonads have lost a classical Golgi during reductive evolution. However, neogenesis of ESVs in encysting Giardia trophozoites transiently provides basic Golgi functions by accumulating presorted CWM exported from the ER for maturation. Based on this “minimal Golgi” hypothesis we predicted maturation of ESVs to a trans Golgi-like stage, which would manifest as a sorting event before regulated secretion of the CWM. Here we show that proteolytic processing of pro-CWP2 in maturing ESVs coincides with partitioning of CWM into two fractions, which are sorted and secreted sequentially with different kinetics. This novel sorting function leads to rapid assembly of a structurally defined outer cyst wall, followed by slow secretion of the remaining components. Using live cell microscopy we find direct evidence for condensed core formation in maturing ESVs. Core formation suggests that a mechanism controlled by phase transitions of the CWM from fluid to condensed and back likely drives CWM partitioning and makes sorting and sequential secretion possible. Blocking of CWP2 processing by a protease inhibitor leads to mis-sorting of a CWP2 reporter. Nevertheless, partitioning and sequential secretion of two portions of the CWM are unaffected in these cells. Although these cysts have a normal appearance they are not water resistant and therefore not infective. Our findings suggest that sequential assembly is a basic architectural principle of protective wall formation and requires minimal Golgi sorting functions.

The protozoan Giardia lamblia is the leading cause for parasite-induced diarrhea with significant morbidity in humans and animals world-wide, and is transmitted by water-resistant cysts. Giardia has undergone substantial reductive evolution to a simpler organization than the last common eukaryotic ancestor, which makes it an interesting model to investigate basic cellular mechanisms. Its secretory system lacks a Golgi, but trophozoites induced to differentiate to cysts generate organelles termed encystation-specific vesicles (ESVs). Previous work shows that ESVs are most likely minimal pulsed Golgi-like compartments for exporting pre-sorted cyst wall material. We tested whether the sorting function associated with classical trans Golgi networks was also conserved in these organelles. By tracking immature and processed forms of the three cyst wall proteins during differentiation we discovered a novel sorting function which results in partitioning of ESV cargo and sequential secretion of the cyst wall material. Using live cell imaging we identified reversible formation of condensed cores as a mechanism for cargo partitioning. These observations suggest that the requirement for sequential secretion of extracellular matrix components protecting Giardia during transmission has prevented the complete secondary loss of the machinery to generate Golgi cisterna-like maturation compartments; indeed, the preserved functions have been placed under stage-specific control.

Glucosylceramide synthesis inhibition affects cell cycle progression, membrane trafficking, and stage differentiation in Giardia lamblia

Synthesis of glucosylceramide via glucosylceramide synthase (GCS) is a crucial event in higher eukaryotes, both for the production of complex glycosphingolipids and for regulating cellular levels of ceramide, a potent antiproliferative second messenger. In this study, we explored the dependence of the early branching eukaryote Giardia lamblia on GCS activity. Biochemical analyses revealed that the parasite has a GCS located in endoplasmic reticulum (ER) membranes that is active in proliferating and encysting trophozoites. Pharmacological inhibition of GCS induced aberrant cell division, characterized by arrest of cytokinesis, incomplete cleavage furrow formation, and consequent block of replication. Importantly, we showed that increased ceramide levels were responsible for the cytokinesis arrest. In addition, GCS inhibition resulted in prominent ultrastructural abnormalities, including accumulation of cytosolic vesicles, enlarged lysosomes, and clathrin disorganization. Moreover, anterograde trafficking of the encystations-specific protein CWP1 was severely compromised and resulted in inhibition of stage differentiation. Our results reveal novel aspects of lipid metabolism in G. lamblia and specifically highlight the vital role of GCS in regulating cell cycle progression, membrane trafficking events, and stage differentiation in this parasite. In addition, we identified ceramide as a potent bioactive molecule, underscoring the universal conservation of ceramide signaling in eukaryotes.

Epigenetic mechanisms regulate stage differentiation in the minimized protozoan Giardia lamblia

Histone modification is an important mechanism regulating both gene expression and the establishment and maintenance of cellular phenotypes during development. Regulation of histone acetylation via histone acetylases and deacetylases (HDACs) appears to be particularly crucial in determining gene expression patterns. In this study we explored the effect of HDAC inhibition on the life cycle of the human pathogen Giardia lamblia, a highly reduced parasitic protozoan characterized by minimized cellular processes. We found that the HDAC inhibitor FR235222 increased the level of histone acetylation and induced transcriptional regulation of approximately 2% of genes in proliferating and encysting parasites. In addition, our analyses showed that the levels of histone acetylation decreased during differentiation into cysts, the infective stage of the parasite. Importantly, FR235222 treatment during encystation reversed this histone hypo-acetylation and potently blocked the formation of cysts. These results provide the first direct evidence for epigenetic regulation of gene expression in this simple eukaryote. This suggests that regulation of histone acetylation is involved in the control of Giardia stage differentiation, and identifies epigenetic mechanisms as a promising target to prevent Giardia transmission.

A contiguous compartment functions as endoplasmic reticulum and endosome/lysosome in Giardia lamblia

The dynamic evolution of organelle compartmentalization in eukaryotes and how strictly compartmentalization is maintained are matters of ongoing debate. While the endoplasmic reticulum (ER) is classically envisioned as the site of protein cotranslational translocation, it has recently been proposed to have pluripotent functions. Using transfected reporter constructs, organelle-specific markers, and functional enzyme assays, we now show that in an early-diverging protozoan, Giardia lamblia, endocytosis and subsequent degradation of exogenous proteins occur in the ER or in an adjacent and communicating compartment. The Giardia endomembrane system is simple compared to those of typical eukaryotes. It lacks peroxisomes, a classical Golgi apparatus, and canonical lysosomes. Giardia orthologues of mammalian lysosomal proteases function within an ER-like tubulovesicular compartment, which itself can dynamically communicate with clathrin-containing vacuoles at the periphery of the cell to receive endocytosed proteins. These primitive characteristics support Giardia's proposed early branching and could serve as a model to study the compartmentalization of endocytic and lysosomal functions into organelles distinct from the ER. This system also may have functional similarity to the retrograde transport of toxins and major histocompatibility complex class I function in the ER of mammals.

Giardia lamblia: a report of drug effects under cell differentiation

The Giardia lamblia life cycle is characterized by two phases during which two major cell differentiation processes take place: encystation and excystation. During encystation, the trophozoites transform into cysts, the resistance form. Once ingested by a susceptible host, the cysts are stimulated to excyst in the stomach, and the excysted trophozoites adhere to the epithelium of the upper small intestine. Our work analyses the effects of four benzimidazole derivatives during Giardia differentiation into cysts and evaluates the excystation efficiency of water resistant cysts. Albendazole (AB) showed the most significant results by inhibiting encystation about 30% and a decreasing rate of excystation efficiency. The ultrastructural organization of the cyst adhesive disk was notably affected by AB treatment. Although other benzimidazoles showed some effect on encystation, they were not able to inhibit the excystation process. It is known that the benzimidazoles affect the cytoskeleton of many organisms but how it interferes in Giardia differentiation processes is our main focus. The importance of studying Giardia's differentiation under drug action is reinforced by the following arguments: (1) Cysts eliminated by hosts undergoing treatment could still be potentially infective; (2) once the host has been treated, it would be desirable that the shedding of cysts into the environment is avoided; (3) the prevention of Giardia dissemination is a question of extreme importance mainly in underdeveloped countries, where poor sanitary conditions are related to high rates of giardiasis. This report concerns the importance of keeping the environment free from infective cysts and on Giardia's drug resistance and differentiating abilities.

Lipidomic analysis reveals that phosphatidylglycerol and phosphatidylethanolamine are newly generated phospholipids in an early-divergent protozoan, Giardia lamblia

The pathogenic protozoan Giardia lamblia is known to not synthesize membrane lipids de novo. Therefore, it is possible that lipids in the small intestine, where trophozoites colonize, play key roles in regulating the growth and differentiation of this important pathogen. The focus of the current study is to conduct a complete lipidomic analysis and to test the hypothesis that Giardia has some ability to generate new phospholipids (PLs). Using mass spectrometry, now we show that phosphatidylglycerols (PGs) are major PLs followed by phosphatidylcholines (PCs) and phosphatidylethanolamines (PEs) in non-encysting and encysting trophozoites, as well in cysts. The fatty acids attached to these PLs consist mostly of palmitate, palmitoleate, oleate, and linoleate. Results also indicate that PGs and PEs, unlike PCs, are not present in bovine bile and serum, the major sources of lipids of the culture medium, and that they could therefore be produced by fatty acid and headgroup remodeling reactions, circumventing the synthesis of entirely new PLs via de novo pathways. Genomic and transcriptional analyses show the presence of giardial phosphatidylglycerolphosphate synthase (gpgps) and phosphatidylserine decarboxylase (gpsd) genes, which are expressed throughout the life cycle. Bioinformatic and phylogenetic analyses further indicated that both genes are of prokaryotic origin and that they have undergone duplication in the course of evolution. Our studies suggest that the abundance of PG in Giardia is unique among eukaryotes and that its synthesis thus could serve as a potential target for developing new therapies against this waterborne parasite.

Novel role of sphingolipid synthesis genes in regulating giardial encystation

Although encystation (cyst formation) is important for the survival of Giardia lamblia outside its human host, the molecular events that prompt encystation have not been fully elucidated. Here, we demonstrate that sphingolipids (SLs), which are important for the growth and differentiation of many eukaryotes, play key roles in giardial encystation. Transcriptional analyses showed that only three genes in the SL biosynthesis pathways are expressed and transcribed differentially in nonencysting and encysting Giardia trophozoites. While the putative homologues of giardial serine palmitoyltransferase (gSPT) subunit genes (gspt-1 and -2) are differentially expressed in nonencysting and encysting trophozoites, the giardial ceramide glucosyltransferase 1 gene (gglct-1) is transcribed only in encysting cells. l-Cycloserine, an inhibitor of gSPT, inhibited the endocytosis and endoplasmic reticulum/perinuclear targeting of bodipy-ceramide in trophozoites, and this could be reversed by 3-ketosphinganine. On the other hand, D-threo-1-phenyl-2-palmitoylamino-3-morpholino-1-propanol (PPMP), an inhibitor of glucosylceramide synthesis, blocked karyokinesis and reduced cyst production in culture. PPMP also altered the expression of cyst wall protein transcripts in encysting cells. Phylogenetic analyses revealed that the gspt genes are paralogs derived from an ancestral spt sequence that underwent gene duplication early in eukaryotic history. This ancestral sequence, in turn, was probably derived from prokaryotic aminoacyl transferases. In contrast, gglct-1 is found in both prokaryotes and eukaryotes without any evidence of gene duplication. These studies indicate that SL synthesis genes are involved in key events in giardial biology and could serve as potential targets for developing new therapies against giardiasis.