Cryptosporidium: genomic and biochemical features

Treating cryptosporidiosis: A review on drug discovery strategies

Despite several decades of research on therapeutics, cryptosporidiosis remains a major concern for human and animal health. Even though this field of research to assess antiparasitic drug activity is highly active and competitive, only one molecule is authorized to be used in humans. However, this molecule was not efficacious in immunocompromised people and the lack of animal therapeutics remains a cause of concern. Indeed, the therapeutic arsenal needs to be developed for both humans and animals. Our work aims to clarify research strategies that historically were diffuse and poorly directed. This paper reviews in vitro and in vivo methodologies to assess the activity of future therapeutic compounds by screening drug libraries or through drug repurposing. It focuses on High Throughput Screening methodologies (HTS) and discusses the lack of knowledge of target mechanisms. In addition, an overview of several specific metabolic pathways and enzymatic activities used as targets against Cryptosporidium is provided. These metabolic processes include glycolytic pathways, fatty acid production, kinase activities, tRNA elaboration, nucleotide synthesis, gene expression and mRNA maturation. As a conclusion, we highlight emerging future strategies for screening natural compounds and assessing drug resistance issues.

Lower micromolar activity of the antifungal imidazoles on the bacterial-type bifunctional aldehyde/alcohol dehydrogenase (AdhE) in Cryptosporidium parvum and in vitro efficacy against the zoonotic parasite

Cryptosporidium parvum is a waterborne and foodborne zoonotic protozoan parasite, a causative agent of moderate to severe diarrheal diseases in humans and animals. However, fully effective treatments are unavailable for medical and veterinary uses. There is a need to explore new drug targets for potential development of new therapeutics. Because C. parvum relies on anaerobic metabolism to produce ATP, fermentative enzymes in this parasite are attractive targets for exploration. In this study, we investigated the ethanol-fermentation in the parasite and characterized the basic biochemical features of a bacterial-type bifunctional aldehyde/alcohol dehydrogenase, namely CpAdhE. We also screened 3892 chemical entries from three libraries and identified 14 compounds showing >50% inhibition on the enzyme activity of CpAdhE. Intriguingly, antifungal imidazoles and unsaturated fatty acids are the two major chemical groups among the top hits. We further characterized the inhibitory kinetics of selected imidazoles and unsaturated fatty acids on CpAdhE. These compounds displayed lower micromolar activities on CpAdhE (i.e., IC50 values ranging from 0.88 to 11.02 μM for imidazoles and 8.93 to 35.33 μM for unsaturated fatty acids). Finally, we evaluated the in vitro anti-cryptosporidial efficacies and cytotoxicity of three imidazoles (i.e., tioconazole, miconazole and isoconazole). The three antifungal imidazoles exhibited lower micromolar efficacies against the growth of C. parvum in vitro (EC50 values ranging from 4.85 to 10.41 μM and selectivity indices ranging from 5.19 to 10.95). The results provide a proof-of-concept data to support that imidazoles are worth being further investigated for potential development of anti-cryptosporidial therapeutics.

Requirement of microtubules for secretion of a micronemal protein CpTSP4 in the invasive stage of the apicomplexan Cryptosporidium parvum

The zoonotic Cryptosporidium parvum is a global contributor to infantile diarrheal diseases and opportunistic infections in immunocompromised or weakened individuals. Like other apicomplexans, it possesses several specialized secretory organelles, including micronemes, rhoptry, and dense granules. However, the understanding of cryptosporidial micronemal composition and secretory pathway remains limited. Here, we report a new micronemal protein in C. parvum, namely, thrombospondin (TSP)-repeat domain-containing protein-4 (CpTSP4), providing insights into these ambiguities. Immunostaining and enzyme-linked assays show that CpTSP4 is prestored in the micronemes of unexcysted sporozoites but secreted during sporozoite excystation, gliding, and invasion. In excysted sporozoites, CpTSP4 is also distributed on the two central microtubules unique to Cryptosporidium. The secretion and microtubular distribution could be completely blocked by the selective kinesin-5 inhibitors SB-743921 and SB-715992, resulting in the accumulation of CpTSP4 in micronemes. These support the kinesin-dependent microtubular trafficking of CpTSP4 for secretion. We also localize γ-tubulin, consistent with kinesin-dependent anterograde trafficking. Additionally, recombinant CpTSP4 displays nanomolar binding affinity to the host cell surface, for which heparin acts as one of the host ligands. A novel heparin-binding motif is identified and validated biochemically for its contribution to the adhesive property of CpTSP4 by peptide competition assays and site-directed mutagenesis. These findings shed light on the mechanisms of intracellular trafficking and secretion of a cryptosporidial micronemal protein and the interaction of a TSP-family protein with host cells.IMPORTANCECryptosporidium parvum is a globally distributed apicomplexan parasite infecting humans and/or animals. Like other apicomplexans, it possesses specialized secretory organelles in the zoites, in which micronemes discharge molecules to facilitate the movement and invasion of zoites. Although past and recent studies have identified several proteins in cryptosporidial micronemes, our understanding of the composition, secretory pathways, and domain-ligand interactions of micronemal proteins remains limited. This study identifies a new micronemal protein, namely, CpTSP4, that is discharged during excystation, gliding, and invasion of C. parvum sporozoites. The CpTSP4 secretion depends on the intracellular trafficking on the two Cryptosporidium-unique microtubes that could be blocked by kinesin-5/Eg5 inhibitors. Additionally, a novel heparin-binding motif is identified and biochemically validated, which contributes to the nanomolar binding affinity of CpTSP4 to host cells. These findings indicate that kinesin-dependent microtubular trafficking is critical to CpTSP4 secretion, and heparin/heparan sulfate is one of the ligands for this micronemal protein.

Multiple pathways for glucose phosphate transport and utilization support growth of Cryptosporidium parvum

Cryptosporidium parvum is an obligate intracellular parasite with a highly reduced mitochondrion that lacks the tricarboxylic acid cycle and the ability to generate ATP, making the parasite reliant on glycolysis. Genetic ablation experiments demonstrated that neither of the two putative glucose transporters CpGT1 and CpGT2 were essential for growth. Surprisingly, hexokinase was also dispensable for parasite growth while the downstream enzyme aldolase was required, suggesting the parasite has an alternative way of obtaining phosphorylated hexose. Complementation studies in E. coli support a role for direct transport of glucose-6-phosphate from the host cell by the parasite transporters CpGT1 and CpGT2, thus bypassing a requirement for hexokinase. Additionally, the parasite obtains phosphorylated glucose from amylopectin stores that are released by the action of the essential enzyme glycogen phosphorylase. Collectively, these findings reveal that C. parvum relies on multiple pathways to obtain phosphorylated glucose both for glycolysis and to restore carbohydrate reserves.

Pyrimidine salvage in Toxoplasma gondii as a target for new treatment

Toxoplasmosis is a common protozoan infection that can have severe outcomes in the immunocompromised and during pregnancy, but treatment options are limited. Recently, nucleotide metabolism has received much attention as a target for new antiprotozoal agents and here we focus on pyrimidine salvage by Toxoplasma gondii as a drug target. Whereas uptake of [3H]-cytidine and particularly [3H]-thymidine was at most marginal, [3H]-uracil and [3H]-uridine were readily taken up. Kinetic analysis of uridine uptake was consistent with a single transporter with a Km of 3.3 ± 0.8 µM, which was inhibited by uracil with high affinity (Ki = 1.15 ± 0.07 µM) but not by thymidine or 5-methyluridine, showing that the 5-Me group is incompatible with uptake by T. gondii. Conversely, [3H]-uracil transport displayed a Km of 2.05 ± 0.40 µM, not significantly different from the uracil Ki on uridine transport, and was inhibited by uridine with a Ki of 2.44 ± 0.59 µM, also not significantly different from the experimental uridine Km. The reciprocal, complete inhibition, displaying Hill slopes of approximately -1, strongly suggest that uridine and uracil share a single transporter with similarly high affinity for both, and we designate it uridine/uracil transporter 1 (TgUUT1). While TgUUT1 excludes 5-methyl substitutions, the smaller 5F substitution was tolerated, as 5F-uracil inhibited uptake of [3H]-uracil with a Ki of 6.80 ± 2.12 µM (P > 0.05 compared to uracil Km). Indeed, we found that 5F-Uridine, 5F-uracil and 5F,2'-deoxyuridine were all potent antimetabolites against T. gondii with EC50 values well below that of the current first line treatment, sulfadiazine. In vivo evaluation also showed that 5F-uracil and 5F,2'-deoxyuridine were similarly effective as sulfadiazine against acute toxoplasmosis. Our preliminary conclusion is that TgUUT1 mediates potential new anti-toxoplasmosis drugs with activity superior to the current treatment.

Cost-effective In Vivo and In Vitro Mouse Models for Evaluating Anticryptosporidial Drug Efficacy: Assessing Vorinostat, Docetaxel, and Baicalein

BACKGROUND

Cryptosporidiosis is a significant diarrheal disease in humans and animals. Immunodeficient mice are the primary small animal models, but their high costs and specialized breeding/housing requirements limit in vivo drug testing. Numerous anticryptosporidial lead compounds identified in vitro remain untested in vivo.

METHODS

Cryptosporidium tyzzeri, a natural mouse parasite closely related to Cryptosporidium parvum and Cryptosporidium hominis, was isolated to establish an infection model in immunocompetent mice. The model was validated using classic anticryptosporidial drugs (paromomycin and nitazoxanide) and then employed to assess the efficacy of 3 new leads (vorinostat, docetaxel, and baicalein). An in vitro culture of C. tyzzeri was also developed to complement the animal model.

RESULTS

Chronic C. tyzzeri infection was established in chemically immunosuppressed wild-type mice. Paromomycin (1000 mg/kg/d) and nitazoxanide (100 mg/kg/d) demonstrated efficacy against C. tyzzeri. Vorinostat (30 mg/kg/d), docetaxel (25 mg/kg/d), and baicalein (50 mg/kg/d) were highly effective against C. tyzzeri infection. In vitro, nitazoxanide, vorinostat, docetaxel, and baicalein exhibited low to submicromolar efficacy against C. tyzzeri.

CONCLUSIONS

Novel in vivo and in vitro models have been developed for cost-effective anticryptosporidial drug testing. Vorinostat, docetaxel, and baicalein show potential for repurposing and/or optimization for developing new anticryptosporidial drugs.

Mass Spectrometry Imaging of In Vitro Cryptosporidium parvum-Infected Cells and Host Tissue

Cryptosporidium parvum is a zoonotic-relevant parasite belonging to the phylum Alveolata (subphylum Apicomplexa). One of the most zoonotic-relevant etiologies of cryptosporidiosis is the species C. parvum, infecting humans, cattle and wildlife. C. parvum-infected intestinal mucosa as well as host cells infected in vitro have not yet been the subject of extensive biochemical investigation. Efficient treatment options or vaccines against cryptosporidiosis are currently not available. Human cryptosporidiosis is currently known as a neglected poverty-related disease (PRD), being potentially fatal in young children or immunocompromised patients. In this study, we used a combination of atmospheric pressure scanning microprobe matrix-assisted laser desorption/ionization (AP-SMALDI) mass spectrometry imaging (MSI) and liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) to determine and locate molecular biomarkers in in vitro C. parvum-infected host cells as well as parasitized neonatal calf intestines. Sections of C. parvum-infected and non-infected host cell pellets and infected intestines were examined to determine potential biomarkers. Human ileocecal adenocarcinoma cells (HCT-8) were used as a suitable in vitro host cell system. More than a thousand different molecular signals were found in both positive- and negative-ion mode, which were significantly increased in C. parvum-infected material. A database search in combination with HPLC-MS/MS experiments was employed for the structural verification of markers. Our results demonstrate some overlap between the identified markers and data obtained from earlier studies on other apicomplexan parasites. Statistically relevant biomarkers were imaged in cell layers of C. parvum-infected and non-infected host cells with 5 µm pixel size and in bovine intestinal tissue with 10 µm pixel size. This allowed us to substantiate their relevance once again. Taken together, the present approach delivers novel metabolic insights on neglected cryptosporidiosis affecting mainly children in developing countries.

High subtelomeric GC content in the genome of a zoonotic Cryptosporidium species

Cryptosporidium canis is a zoonotic species causing cryptosporidiosis in humans in addition to its natural hosts dogs and other fur animals. To understand the genetic basis for host adaptation, we sequenced the genomes of C. canis from dogs, minks, and foxes and conducted a comparative genomics analysis. While the genomes of C. canis have similar gene contents and organisations, they (~41.0 %) and C. felis (39.6 %) have GC content much higher than other Cryptosporidium spp. (24.3-32.9 %) sequenced to date. The high GC content is mostly restricted to subtelomeric regions of the eight chromosomes. Most of these GC-balanced genes encode Cryptosporidium-specific proteins that have intrinsically disordered regions and are involved in host-parasite interactions. Natural selection appears to play a more important role in the evolution of codon usage in GC-balanced C. canis, and most of the GC-balanced genes have undergone positive selection. While the identity in whole genome sequences between the mink- and dog-derived isolates is 99.9 % (9365 SNVs), it is only 96.0 % (362 894 SNVs) between them and the fox-derived isolate. In agreement with this, the fox-derived isolate possesses more subtelomeric genes encoding invasion-related protein families. Therefore, the change in subtelomeric GC content appears to be responsible for the more GC-balanced C. canis genomes, and the fox-derived isolate could represent a new Cryptosporidium species.

Multiple pathways for glucose phosphate transport and utilization support growth of Cryptosporidium parvum

Cryptosporidium parvum is an obligate intracellular parasite with a highly reduced mitochondrion that lacks the TCA cycle and the ability to generate ATP, making the parasite reliant on glycolysis. Genetic ablation experiments demonstrated that neither of the two putative glucose transporters CpGT1 and CpGT2 were essential for growth. Surprisingly, hexokinase was also dispensable for parasite growth while the downstream enzyme aldolase was required, suggesting the parasite has an alternative way of obtaining phosphorylated hexose. Complementation studies in E. coli support a role for direct transport of glucose-6-phosphate from the host cell by the parasite transporters CpGT1 and CpGT2, thus bypassing a requirement for hexokinase. Additionally, the parasite obtains phosphorylated glucose from amylopectin stores that are released by the action of the essential enzyme glycogen phosphorylase. Collectively, these findings reveal that C. parvum relies on multiple pathways to obtain phosphorylated glucose both for glycolysis and to restore carbohydrate reserves.

Genomic reconstruction and features of glycosylation pathways in the apicomplexan Cryptosporidium parasites

Cryptosporidium is a genus of apicomplexan parasites infecting humans or other vertebrates. The majority of the Cryptosporidium species live in host intestines (e.g., C. parvum, C. hominis and C. ubiquitum), but there are a few gastric species (e.g., C. muris and C. andersoni). Among them, C. parvum is the most important zoonotic species, for which a number of glycoproteins have been reported for being involved in the interacting with host cells. However, little is known on the cryptosporidium glycobiology. Information on the glycosylation pathways in Cryptosporidium parasites remains sketchy and only a few studies have truly determined the glycoforms in the parasites. Here we reanalyzed the Cryptosporidium genomes and reconstructed the glycosylation pathways, including the synthesis of N- and O-linked glycans and GPI-anchors. In N-glycosylation, intestinal Cryptosporidium possesses enzymes to make a simple precursor with two terminal glucoses on the long arm (i.e., Glc2Man5GlcNAc2 vs. Glc3Man9GlcNAc2 in humans), but gastric species only makes a simpler precursor containing only the "core" structure (i.e., Man3GlcNAc2). There is an ortholog of glucosidase II (GANAB) in all Cryptosporidium species, for which the authenticity is questioned because it contains no signal peptide and exist in gastric species lacking terminal glucoses for the enzyme to act on. In O-linked glycosylation, all Cryptosporidium species may attach one-unit HexNAc (GalNAc and GlcNAc) and two-unit Fuc-type (Man-Fuc) glycans to the target proteins. Cryptosporidium lacks enzymes to further process N- and O-glycans in the Golgi. The glycosylphosphatidylinositol (GPI)-anchor in Cryptosporidium is predicted to be unbranched and unprocessed further in the Golgi. Cryptosporidium can synthesize limited nucleotide sugars, but possesses at least 12 transporters to scavenge nucleotide sugars or transport them across the ER/Golgi membranes. Overall, Cryptosporidium makes much simpler glycans than the hosts, and the N-glycoforms further differ between intestinal and gastric species. The Cryptosporidium N- and O-glycans are neutrally charged and have limited capacity to absorb water molecules in comparison to the host intestinal mucins that are negatively charged and highly expandable in waters.

Putative SET-domain methyltransferases in Cryptosporidium parvum and histone methylation during infection

Cryptosporidium parvum is a leading cause of diarrhoeal illness worldwide being a significant threat to young children and immunocompromised patients, but the pathogenesis caused by this parasite remains poorly understood. C. parvum was recently linked with oncogenesis. Notably, the mechanisms of gene expression regulation are unexplored in Cryptosporidium and little is known about how the parasite impact host genome regulation. Here, we investigated potential histone lysine methylation, a dynamic epigenetic modification, during the life cycle of the parasite. We identified SET-domain containing proteins, putative lysine methyltransferases (KMTs), in the C. parvum genome and classified them phylogenetically into distinct subfamilies (namely CpSET1, CpSET2, CpSET8, CpKMTox and CpAKMT). Our structural analysis further characterized CpSET1, CpSET2 and CpSET8 as histone lysine methyltransferases (HKMTs). The expression of the CpSET genes varies considerably during the parasite life cycle and specific methyl-lysine antibodies showed dynamic changes in parasite histone methylation during development (CpSET1:H3K4; CpSET2:H3K36; CpSET8:H4K20). We investigated the impact of C. parvum infection on the host histone lysine methylation. Remarkably, parasite infection led to a considerable decrease in host H3K36me3 and H3K27me3 levels, highlighting the potential of the parasite to exploit the host epigenetic regulation to its advantage. This is the first study to describe epigenetic mechanisms occurring throughout the parasite life cycle and during the host–parasite interaction. A better understanding of histone methylation in both parasite and host genomes may highlight novel infection control strategies.

Implication of Potential Differential Roles of the Two Phosphoglucomutase Isoforms in the Protozoan Parasite Cryptosporidium parvum

Phosphoglucomutase 1 (PGM1) catalyzes the conversion between glucose-1-phosphate and glucose-6-phosphate in the glycolysis/glucogenesis pathway. PGM1s are typically cytosolic enzymes in organisms lacking chloroplasts. However, the protozoan Cryptosporidium parasites possess two tandemly duplicated PGM1 genes evolved by a gene duplication after their split from other apicomplexans. Moreover, the downstream PGM1 isoform contains an N-terminal signal peptide, predicting a non-cytosolic location. Here we expressed recombinant proteins of the two PGM1 isoforms from the zoonotic Cryptosporidium parvum, namely CpPGM1A and CpPGM1B, and confirmed their enzyme activity. Both isoforms followed Michaelis–Menten kinetics towards glucose-1-phosphate (K_m = 0.17 and 0.13 mM, V_max = 7.30 and 2.76 μmol/min/mg, respectively). CpPGM1A and CpPGM1B genes were expressed in oocysts, sporozoites and intracellular parasites at a similar pattern of expression, however CpPGM1A was expressed at much higher levels than CpPGM1B. Immunofluorescence assay showed that CpPGM1A was present in the cytosol of sporozoites, however this was enriched towards the plasma membranes in the intracellular parasites; whereas CpPGM1B was mainly present under sporozoite pellicle, although relocated to the parasitophorous vacuole membrane in the intracellular development. These observations indicated that CpPGM1A played a house-keeping function, while CpPGM1B played a different biological role that remains to be defined by future investigations.

Dual transcriptomics to determine interferon-gamma independent host response to intestinal Cryptosporidium parvum infection

Animals with a chronic infection of the parasite Toxoplasma gondii are protected against lethal secondary infection with other pathogens. Our group previously determined that soluble T. gondii antigens (STAg) can mimic this protection and be used as a treatment against several lethal pathogens. Because treatments are limited for the parasite Cryptosporidium parvum, we tested STAg as a C. parvum therapeutic. We determined that STAg treatment reduced C. parvum Iowa II oocyst shedding in gamma interferon knockout (IFN-γ-KO) mice. Murine intestinal sections were then sequenced to define the IFN-γ-independent transcriptomic response to C. parvum infection. Gene Ontology and transcript abundance comparisons showed host immune response and metabolism changes. Transcripts for type I interferon-responsive genes were more abundant in C. parvum-infected mice treated with STAg. Comparisons between phosphate-buffered saline (PBS) and STAg treatments showed no significant differences in C. parvum gene expression. C. parvum transcript abundance was highest in the ileum and mucin-like glycoproteins and the GDP-fucose transporter were among the most abundant. These results will assist the field in determining both host- and parasite-directed future therapeutic targets.

Cryptosporidium felis differs from other Cryptosporidium spp. in codon usage

Cryptosporidium spp. are important enteric pathogens in a wide range of vertebrates including humans. Previous comparative analysis revealed conservation in genome composition, gene content, and gene organization among Cryptosporidium spp., with a progressive reductive evolution in metabolic pathways and invasion-related proteins. In this study, we sequenced the genome of zoonotic pathogen Cryptosporidium felis and conducted a comparative genomic analysis. While most intestinal Cryptosporidium species have similar genomic characteristics and almost complete genome synteny, fewer protein-coding genes and some sequence inversions and translocations were found in the C. felis genome. The C. felis genome exhibits much higher GC content (39.6 %) than other Cryptosporidium species (24.3–32.9 %), especially at the third codon position (GC3) of protein-coding genes. Thus, C. felis has a different codon usage, which increases the use of less energy costly amino acids (Gly and Ala) encoded by GC-rich codons. While the tRNA usage is conserved among Cryptosporidium species, consistent with its higher GC content, C. felis uses a unique tRNA for GTG for valine instead of GTA in other Cryptosporidium species. Both mutational pressures and natural selection are associated with the evolution of the codon usage in Cryptosporidium spp., while natural selection seems to drive the codon usage in C. felis. Other unique features of the C. felis genome include the loss of the entire traditional and alternative electron transport systems and several invasion-related proteins. Thus, the preference for the use of some less energy costly amino acids in C. felis may lead to a more harmonious parasite–host interaction, and the strengthened host-adaptation is reflected by the further reductive evolution of metabolism and host invasion-related proteins.

In Silico Identification and Functional Characterization of Conserved miRNAs in the Genome of Cryptosporidium parvum

Cryptosporidium parvum, a predominant causal agent of a fatal zoonotic protozoan diarrhoeal disease called cryptosporidiosis, bears a worldwide public health concern for childhood mortality and poses a key threat to the dairy and water industries. MicroRNAs (miRNAs), small but powerful posttranscriptional gene silencing RNA molecules, regulate a variety of molecular, biological, and cellular processes in animals and plants. As to the present date, there is a paucity of information regarding miRNAs of C. parvum; hence, this study was used to identify miRNAs in the organism using a comprehensible expressed sequence tag-based homology search approach consisting of a series of computational screening process from the identification of putative miRNA candidates to the functional annotation of the important gene targets in C. parvum. The results revealed a conserved miRNA that targeted 487 genes in the model organism (Drosophila melanogaster) and 85 genes in C. parvum, of which 11 genes had direct involvements in several crucial virulence factors such as environmental oocyst protection, excystation, locomotion, adhesion, invasion, stress protection, intracellular growth, and survival. Besides, 20 genes showed their association with various major pathways dedicated for the ribosomal biosynthesis, DNA repair, transportation, protein production, gene expression, cell cycle, cell proliferation, development, immune response, differentiation, and nutrient metabolism of the organism in the host. Thus, this study provides a strong evidence of great impact of identified miRNA on the biology, virulence, and pathogenesis of C. parvum. Furthermore, the study suggests that the detected miRNA could be a potential epigenomic tool for controlling the protozoon through silencing those virulent and pathway-related target genes.

Serum metabolomics in chickens infected with Cryptosporidium baileyi

Background

Cryptosporidium baileyi is an economically important zoonotic pathogen that causes serious respiratory symptoms in chickens for which no effective control measures are currently available. An accumulating body of evidence indicates the potential and usefulness of metabolomics to further our understanding of the interaction between pathogens and hosts, and to search for new diagnostic or pharmacological biomarkers of complex microorganisms. The aim of this study was to identify the impact of C. baileyi infection on the serum metabolism of chickens and to assess several metabolites as potential diagnostic biomarkers for C. baileyi infection.

Methods

Ultraperformance liquid chromatography-mass spectrometry (UPLC-MS) and subsequent multivariate statistical analysis were applied to investigate metabolomics profiles in the serum samples of chickens infected with C. baileyi, and to identify potential metabolites that can be used to distinguish chickens infected with C. baileyi from non-infected birds.

Results

Multivariate statistical analysis identified 138 differential serum metabolites between mock- and C. baileyi-infected chickens at 5 days post-infection (dpi), including 115 upregulated and 23 downregulated compounds. These metabolites were significantly enriched into six pathways, of which two pathways associated with energy and lipid metabolism, namely glycerophospholipid metabolism and sphingolipid metabolism, respectively, were the most enriched. Interestingly, some important immune-related pathways were also significantly enriched, including the intestinal immune network for IgA production, autophagy and cellular senescence. Nine potential C. baileyi-responsive metabolites were identified, including choline, sirolimus, all-trans retinoic acid, PC(14:0/22:1(13Z)), PC(15:0/22:6(4Z,7Z,10Z,13Z,16Z,19Z)), PE(16:1(9Z)/24:1(15Z)), phosphocholine, SM(d18:0/16:1(9Z)(OH)) and sphinganine.

Conclusions

This is the first report on serum metabolic profiling of chickens with early-stage C. baileyi infection. The results provide novel insights into the pathophysiological mechanisms of C. baileyi in chickens.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04834-y.

Current status and challenges in drug discovery against the globally important zoonotic cryptosporidiosis

The zoonotic cryptosporidiosis is globally distributed, one of the major diarrheal diseases in humans and animals. Cryptosporidium oocysts are also one of the major environmental concerns, making it a pathogen that fits well into the One Health concept. Despite its importance, fully effective drugs are not yet available. Anti-cryptosporidial drug discovery has historically faced many unusual challenges attributed to unique parasite biology and technical burdens. While significant progresses have been made recently, anti-cryptosporidial drug discovery still faces a major obstacle: identification of systemic drugs that can be absorbed by patients experiencing watery diarrhea and effectively pass through electron-dense (ED) band at the parasite-host cell interface to act on the epicellular parasite. There may be a need to develop an in vitro assay to effectively screen hits/leads for their capability to cross ED band. In the meantime, non-systemic drugs with strong mucoadhesive properties for extended gastrointestinal exposure may represent another direction in developing anti-cryptosporidial therapeutics. For developing both systemic and non-systemic drugs, a non-ruminant animal model exhibiting diarrheal symptoms suitable for routine evaluation of drug absorption and anti-cryptosporidial efficacy may be very helpful.

Insulinase-like Protease 1 Contributes to Macrogamont Formation in Cryptosporidium parvum

The apicomplexan parasite Cryptosporidium parvum contains an expanded family of 22 insulinase-like proteases (INS), a feature that contrasts with their otherwise streamlined genome. Here, we examined the function of INS1, which is most similar to the human insulinase protease that cleaves a variety of small peptide substrates. INS1 is an M16A clan member and contains a signal peptide, an N-terminal domain with the HXXEH active site, followed by three inactive domains. Unlike previously studied C. parvum INS proteins that are expressed in sporozoites and during merogony, INS1 was expressed exclusively in macrogamonts, where it was localized in small cytoplasmic vesicles. Although INS1 did not colocalize with the oocyst wall protein recognized by the antibody OW50, immune-electron microscopy indicated that INS1 resides in small vesicles in the secretory system. Notably, these small INS1-positive vesicles were often in close proximity to large OW50-positive vacuoles resembling wall-forming bodies, which contain precursors for oocyst wall formation. Genetic deletion of INS1, or replacement with an active-site mutant, resulted in lower formation of macrogamonts in vitro and reduced oocyst shedding in vivo Our findings reveal that INS1 functions in the formation or maturation of macrogamonts and that its loss results in attenuated virulence in immunocompromised mice.IMPORTANCE Cryptosporidiosis is a debilitating diarrheal disease in young children in developing countries. The absence of effective treatments or vaccines makes this infection very difficult to manage in susceptible populations. Although the oral dose of oocysts needed to cause infection is low, infected individuals shed very high numbers of oocysts, readily contaminating the environment. Our studies demonstrate that the protease INS1 is important for formation of female sexual stages and that in its absence, parasites produce fewer oocysts and are attenuated in immunocompromised mice. These findings suggest that mutants lacking INS1, or related proteases, are useful for further characterizing the pathway that leads to macrogamont maturation and oocyst wall formation.

Cryptosporidium: Host-Parasite Interactions and Pathogenesis

Purpose of Review

Cryptosporidium spp. (C. hominis and C. parvum) are a major cause of diarrhea-associated morbidity and mortality in young children globally. While C. hominis only infects humans, C. parvum is a zoonotic parasite that can be transmitted from infected animals to humans. There are no treatment or control measures to fully treat cryptosporidiosis or prevent the infection in humans and animals. Our knowledge on the molecular mechanisms of Cryptosporidium-host interactions and the underlying factors that govern infectivity and disease pathogenesis is very limited.

Recent Findings

Recent development of genetics and new animal models of infection, along with progress in cell culture platforms to complete the parasite lifecycle in vitro, is greatly advancing the Cryptosporidium field.

Summary

In this review, we will discuss our current knowledge of host-parasite interactions and how genetic manipulation of Cryptosporidium and promising infection models are opening the doors towards an improved understanding of parasite biology and disease pathogenesis.

Neonatal Mouse Gut Metabolites Influence Cryptosporidium parvum Infection in Intestinal Epithelial Cells

Cryptosporidium sp. occupies a unique intracellular niche that exposes the parasite to both host cell contents and the intestinal lumen, including metabolites from the diet and produced by the microbiota. Both dietary and microbial products change over the course of early development and could contribute to the changes seen in susceptibility to cryptosporidiosis in humans and mice.

The protozoan parasite Cryptosporidium sp. is a leading cause of diarrheal disease in those with compromised or underdeveloped immune systems, particularly infants and toddlers in resource-poor localities. As an enteric pathogen, Cryptosporidium sp. invades the apical surface of intestinal epithelial cells, where it resides in close proximity to metabolites in the intestinal lumen. However, the effect of gut metabolites on susceptibility to Cryptosporidium infection remains largely unstudied. Here, we first identified which gut metabolites are prevalent in neonatal mice when they are most susceptible to Cryptosporidium parvum infection and then tested the isolated effects of these metabolites on C. parvum invasion and growth in intestinal epithelial cells. Our findings demonstrate that medium or long-chain saturated fatty acids inhibit C. parvum growth, perhaps by negatively affecting the streamlined metabolism in C. parvum, which is unable to synthesize fatty acids. Conversely, long-chain unsaturated fatty acids enhanced C. parvum invasion, possibly by modulating membrane fluidity. Hence, gut metabolites, either from diet or produced by the microbiota, influence C. parvum growth in vitro and may also contribute to the early susceptibility to cryptosporidiosis seen in young animals.

Cryptosporidium parvum alters glucose transport mechanisms in infected enterocytes

The parasite Cryptosporidium parvum Tyzzer 1912 destroys parts of the intestinal brush border membrane which is important for the uptake of nutrients like glucose. In this study, glucose transport mechanisms of the host cells (IPEC-J2 cells) infected by C. parvum were investigated. The mRNA expression levels of glucose transporters (GLUT) 1 and 2 and Na⁺-coupled glucose transporter (SGLT) 1 were compared in infected and uninfected cells over an infection time of 24-96 h by RT-qPCR. Furthermore, the protein expression of SGLT 1 and GLUT 2 was quantified in western blot studies. While the protein expression of SGLT 1 was not altered in infected cells, mRNA expression of SGLT 1 and GLUT 1 was significantly increased 24 h p. i. and decreased 96 h p. i. The mRNA expression of GLUT 2 was significantly decreased 24 h, 72 h, and 96 h p. i. and also correlated significantly with the infection dose at 72 h p. i. In contrast to that, the protein expression of GLUT 2 was significantly increased 48 h p. i., associated with a significantly higher intracellular glucose level in infected cells compared with control cells at that time point of infection. This points to an adaptation of the host cells' glucose uptake taking place in the acute phase of the infection. A better understanding of these molecular mechanisms following a C. parvum infection may probably lead to an improvement of therapy strategies in the future.

The Existing Drug Vorinostat as a New Lead Against Cryptosporidiosis by Targeting the Parasite Histone Deacetylases

Background

Cryptosporidiosis affects all human populations, but can be much more severe or life-threatening in children and individuals with weak or weakened immune systems. However, current options to treat cryptosporidiosis are limited.

Methods

An in vitro phenotypic screening assay was employed to screen 1200 existing drugs for their anticryptosporidial activity and to determine the inhibitory kinetics of top hits. Selected top hits were further evaluated in mice. The action of the lead compound vorinostat on the parasite histone deacetylase (HDAC) was biochemically validated.

Results

Fifteen compounds exhibited anticryptosporidial activity at nanomolar level in vitro. Among them, the histone deacetylase (HDAC) inhibitor vorinostat retained outstanding efficacy in vitro (half maximal effective concentration, EC50 = 203 nM) and in an interleukin 12 knockout mouse model (50% inhibition dose = 7.5 mg/kg). Vorinostat was effective on various parasite developmental stages and could irreversibly kill the parasite. Vorinostat was highly effective against the parasite native HDAC enzymes (half maximal inhibitory concentration, IC50 = 90.0 nM) and a recombinant Cryptosporidium parvum HDAC (the inhibitor constant, Ki = 123.0 nM).

Conclusions

These findings suggest the potential for repurposing of vorinostat to treat cryptosporidiosis, and imply that the parasite HDAC can be explored for developing more selective anticryptosporidial therapeutics.

The Action of the Hexokinase Inhibitor 2-deoxy-d-glucose on Cryptosporidium parvum and the Discovery of Activities against the Parasite Hexokinase from Marketed Drugs

Cryptosporidium parvum is one of the major species causing mild to severe cryptosporidiosis in humans and animals. We have previously observed that 2-deoxy-d-glucose (2DG) could inhibit both the enzyme activity of C. parvum hexokinase (CpHK) and the parasite growth in vitro. However, the action and fate of 2DG in C. parvum was not fully investigated. In the present study, we showed that, although 2DG could be phosphorylated by CpHK to form 2DG-6-phosphate (2DG6P), the anti-cryptosporidial activity of 2DG was mainly attributed to the action of 2DG on CpHK, rather than the action of 2DG or 2DG6P on the downstream enzyme glucose-6-phosphate isomerase (CpGPI) nor 2DG6P on CpHK. These observations further supported the hypothesis that CpHK could serve as a drug target in the parasite. We also screened 1,200 small molecules consisting of marketed drugs against CpHK, from which four drugs were identified as CpHK inhibitors with micromolar level of anti-cryptospordial activities at concentrations nontoxic to the host cells (i.e. hexachlorphene, thimerosal, alexidine dihydrochloride, and ebselen with EC₅₀  = 0.53, 1.77, 8.1 and 165 μM, respectively). The anti-CpHK activity of the four existing drugs provided us new reagents for studying the enzyme properties of the parasite hexokinase.

Discovery of ebselen as an inhibitor of Cryptosporidium parvum glucose-6-phosphate isomerase (CpGPI) by high-throughput screening of existing drugs

Cryptosporidium parvum is a water-borne and food-borne apicomplexan pathogen. It is one of the top four diarrheal-causing pathogens in children under the age of five in developing countries, and an opportunistic pathogen in immunocompromised individuals. Unlike other apicomplexans, C. parvum lacks Kreb's cycle and cytochrome-based respiration, thus relying mainly on glycolysis to produce ATP. In this study, we characterized the primary biochemical features of the C. parvum glucose-6-phosphate isomerase (CpGPI) and determined its Michaelis constant towards fructose-6-phosphate (K_m = 0.309 mM, V_max = 31.72 nmol/μg/min). We also discovered that ebselen, an organoselenium drug, was a selective inhibitor of CpGPI by high-throughput screening of 1200 known drugs. Ebselen acted on CpGPI as an allosteric noncompetitive inhibitor (IC₅₀ = 8.33 μM; K_i = 36.33 μM), while complete inhibition of CpGPI activity was not achieved. Ebselen could also inhibit the growth of C. parvum in vitro (EC₅₀ = 165 μM) at concentrations nontoxic to host cells, albeit with a relatively small in vitro safety window of 4.2 (cytotoxicity TC₅₀ on HCT-8 cells = 700 μM). Additionally, ebselen might also target other enzymes in the parasite, leading to the parasite growth reduction. Therefore, although ebselen is useful in studying the inhibition of CpGPI enzyme activity, further proof is needed to chemically and/or genetically validate CpGPI as a drug target.

•

Cryptosporidium parvum possesses a single glucose-6-phosphate isomerase (CpGPI).

•

CpGPI displays Michaelis-Menten kinetics towards fructose-6P (K_m = 0.309 mM).

•

The organoselenium ebselen is a CpGPI inhibitor identified from 1200 existing drugs.

•

Ebselen displays allosteric noncompetitive inhibition on CpGPI (K_i = 36.33 μM).

•

Ebeselen could inhibit the growth of C. parvum in vitro (EC₅₀ = 165 μM).

Immunolocation and enzyme activity analysis of Cryptosporidium parvum enolase

Background

Enolase is an essential multifunctional glycolytic enzyme that is involved in many biological processes of apicomplexan protozoa, such as adhesion and invasion. However, the characteristics of enolase in Cryptosporidium parvum, including the location on the oocyst and the enzyme activity, remain unclear.

Methods

The C. parvum enolase gene (cpeno) was amplified by RT-PCR and sequenced. The deduced amino acid sequence was analysed by bioinformatics software. The gene was expressed in Escherichia coli BL21 (DE3) and purified recombinant protein was used for enzyme activity analysis, binding experiments and antibody preparation. The localisation of enolase on oocysts was examined via immunofluorescence techniques.

Results

A 1,350 bp DNA sequence was amplified from cDNA taken from C. parvum oocysts. The deduced amino acids sequence of C. parvum enolase (CpEno) had 82.1% homology with Cryptosporidium muris enolase, and 54.7–68.0% homology with others selected species. Western blot analysis indicated that recombinant C. parvum enolase (rCpEno) could be recognised by C. parvum-infected cattle sera. Immunolocalization testing showed that CpEno was found to locate mainly on the surface of oocysts. The enzyme activity was 33.5 U/mg, and the Michaelis constant (K_m) was 0.571 mM/l. Kinetic measurements revealed that the most suitable pH value was 7.0–7.5, and there were only minor effects on the activity of rCpEno with a change in the reaction temperature. The enzyme activity decreased when the Ca²⁺, K⁺, Mg²⁺ and Na⁺ concentrations of the reaction solution increased. The binding assays demonstrated that rCpEno could bind to human plasminogen.

Conclusion

This study is the first report of immunolocation, binding activity and enzyme characteristics of CpEno. The results of this study suggest that the surface-associated CpEno not only functions as a glycolytic enzyme but may also participate in attachment and invasion process of the parasite.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2200-y) contains supplementary material, which is available to authorized users.

In silico identification and validation of a novel hypothetical protein in Cryptosporidium hominis and virtual screening of inhibitors as therapeutics

Computational approaches to predict structure/function and other biological characteristics of proteins are becoming more common in comparison to the traditional methods in drug discovery. Cryptosporidiosis is a major zoonotic diarrheal disease particularly in children, which is caused primarily by Cryptosporidium hominis and Cryptosporidium parvum. Currently, there are no vaccines for cryptosporidiosis and recommended drugs are ineffective. With the availability of complete genome sequence of C. hominis, new targets have been recognized for the development of effective and better drugs and/or vaccines. We identified a unique hypothetical protein (TU502HP) in the C. hominis genome from the CryptoDB database. A three-dimensional model of the protein was generated using the Iterative Threading ASSEmbly Refinement server through an iterative threading method. Functional annotation and phylogenetic study of TU502HP protein revealed similarity with human transportin 3. The model is further subjected to a virtual screening study form the ZINC database compound library using the Dock Blaster server. A docking study through AutoDock software reported N-(3-chlorobenzyl)ethane-1,2-diamine as the best inhibitor in terms of docking score and binding energy. The reliability of the binding mode of the inhibitor is confirmed by a complex molecular dynamics simulation study using GROMACS software for 10 ns in the water environment. Furthermore, antigenic determinants of the protein were determined with the help of DNASTAR software. Our findings report a great potential in order to provide insights in the development of new drug(s) or vaccine(s) for treatment and prophylaxis of cryptosporidiosis among humans and animals.

Inhibition of Calcium-Dependent Protein Kinase 1 (CDPK1) In Vitro by Pyrazolopyrimidine Derivatives Does Not Correlate with Sensitivity of Cryptosporidium parvum Growth in Cell Culture

Cryptosporidiosis is a serious diarrheal disease in immunocompromised patients and malnourished children, and treatment is complicated by a lack of adequate drugs. Recent studies suggest that the natural occurrence of a small gatekeeper residue in serine threonine calcium-dependent protein kinase 1 (CDPK1) of Cryptosporidium parvum might be exploited to target this enzyme and block parasite growth. Here were explored the potency with which a series of pyrazolopyrimidine analogs, which are selective for small gatekeeper kinases, inhibit C. parvum CDPK1 and block C. parvum growth in tissue culture in vitro. Although these compounds potently inhibited kinase activity in vitro, most had no effect on parasite growth. Moreover, among those that were active against parasite growth, there was a very poor correlation with their 50% inhibitory concentrations against the enzyme. Active compounds also had no effect on cell invasion, unlike the situation in Toxoplasma gondii, where these compounds block CDPK1, prevent microneme secretion, and disrupt cell invasion. These findings suggest that CPDK1 is not essential for C. parvum host cell invasion or growth and therefore that it is not the optimal target for therapeutic intervention. Nonetheless, several inhibitors with low micromolar 50% effective concentrations were identified, and these may affect other essential targets in C. parvum that are worthy of further exploration.

Differential Gene Expression and Protein Localization of Cryptosporidium parvum Fatty Acyl-CoA Synthetase Isoforms

Cryptosporidium parvum is unable to synthesize fatty acids de novo, but possesses three long-chain fatty acyl-CoA synthetase (CpACS) isoforms for activating fatty acids. We have recently shown that these enzymes could be targeted to kill the parasite in vitro and in vivo. Here, we demonstrated that the CpACS genes were differentially expressed during the parasite life cycle, and their proteins were localized to different subcellular structures by immunofluorescence and immuno-electron microscopies. Among them, CpACS1 displayed as an apical protein in sporozoites and merozoites, but no or little presence during the intracellular merogony until the release of merozoites, suggesting that CpACS1 probably functioned mainly during the parasite invasion and/or early stage of intracellular development. Both CpACS2 and CpACS3 proteins were present in all parasite life cycle stages, in which CpACS2 was present in the parasite and the parasitophorous vacuole membranes (PVM), whereas CpACS3 was mainly present in the parasite plasma membranes with little presence in the PVM. These observations suggest that CpACS2 and CpACS3 may participate in scavenging and transport of fatty acids across the PVM and the parasite cytoplasmic membranes, respectively.

Isolation and enrichment of Cryptosporidium DNA and verification of DNA purity for whole-genome sequencing

Whole-genome sequencing of Cryptosporidium spp. is hampered by difficulties in obtaining sufficient, highly pure genomic DNA from clinical specimens. In this study, we developed procedures for the isolation and enrichment of Cryptosporidium genomic DNA from fecal specimens and verification of DNA purity for whole-genome sequencing. The isolation and enrichment of genomic DNA were achieved by a combination of three oocyst purification steps and whole-genome amplification (WGA) of DNA from purified oocysts. Quantitative PCR (qPCR) analysis of WGA products was used as an initial quality assessment of amplified genomic DNA. The purity of WGA products was assessed by Sanger sequencing of cloned products. Next-generation sequencing tools were used in final evaluations of genome coverage and of the extent of contamination. Altogether, 24 fecal specimens of Cryptosporidium parvum, C. hominis, C. andersoni, C. ubiquitum, C. tyzzeri, and Cryptosporidium chipmunk genotype I were processed with the procedures. As expected, WGA products with low (<16.0) threshold cycle (CT) values yielded mostly Cryptosporidium sequences in Sanger sequencing. The cloning-sequencing analysis, however, showed significant contamination in 5 WGA products (proportion of positive colonies derived from Cryptosporidium genomic DNA, ≤25%). Following this strategy, 20 WGA products from six Cryptosporidium species or genotypes with low (mostly <14.0) CT values were submitted to whole-genome sequencing, generating sequence data covering 94.5% to 99.7% of Cryptosporidium genomes, with mostly minor contamination from bacterial, fungal, and host DNA. These results suggest that the described strategy can be used effectively for the isolation and enrichment of Cryptosporidium DNA from fecal specimens for whole-genome sequencing.

A review of the global burden, novel diagnostics, therapeutics, and vaccine targets for cryptosporidium

Cryptosporidium spp are well recognised as causes of diarrhoeal disease during waterborne epidemics and in immunocompromised hosts. Studies have also drawn attention to an underestimated global burden and suggest major gaps in optimum diagnosis, treatment, and immunisation. Cryptosporidiosis is increasingly identified as an important cause of morbidity and mortality worldwide. Studies in low-resource settings and high-income countries have confirmed the importance of cryptosporidium as a cause of diarrhoea and childhood malnutrition. Diagnostic tests for cryptosporidium infection are suboptimum, necessitating specialised tests that are often insensitive. Antigen-detection and PCR improve sensitivity, and multiplexed antigen detection and molecular assays are underused. Therapy has some effect in healthy hosts and no proven efficacy in patients with AIDS. Use of cryptosporidium genomes has helped to identify promising therapeutic targets, and drugs are in development, but methods to assess the efficacy in vitro and in animals are not well standardised. Partial immunity after exposure suggests the potential for successful vaccines, and several are in development; however, surrogates of protection are not well defined. Improved methods for propagation and genetic manipulation of the organism would be significant advances.

A unique hexokinase in Cryptosporidium parvum, an apicomplexan pathogen lacking the Krebs cycle and oxidative phosphorylation

Cryptosporidium parvum may cause virtually untreatable infections in AIDS patients, and is recently identified as one of the top four diarrheal pathogens in children in developing countries. Cryptosporidium differs from other apicomplexans (e.g., Plasmodium and Toxoplasma) by lacking many metabolic pathways including the Krebs cycle and cytochrome-based respiratory chain, thus relying mainly on glycolysis for ATP production. Here we report the molecular and biochemical characterizations of a hexokinase in C. parvum (CpHK). Our phylogenetic reconstructions indicated that apicomplexan hexokinases including CpHK were highly divergent from those of humans and animals (i.e., at the base of the eukaryotic clade). CpHK displays unique kinetic features that differ from those in mammals and Toxoplasma gondii (TgHK) in the preference towards various hexoses and its capacity to use ATP and other NTPs. CpHK also displays substrate inhibition by ATP. Moreover, 2-deoxy-D-glucose (2DG) could not only inhibit the CpHK activity, but also the parasite growth in vitro at concentrations nontoxic to host cells (IC(50) = 0.54 mM). While the exact action of 2-deoxy-D-glucose on the parasite is subject to further verification, our data suggest that CpHK and the glycolytic pathway may be explored for developing anti-cryptosporidial therapeutics.

Cryptosporidiuminfections: molecular advances

Cryptosporidiumhost cell interaction remains fairly obscure compared with other apicomplexans such asPlasmodiumorToxoplasma. The reason for this is probably the inability of this parasite to complete its life cyclein vitroand the lack of a system to genetically modifyCryptosporidium. However, there is a substantial set of data about the molecules involved in attachment and invasion and about the host cell pathways involved in actin arrangement that are altered by the parasite. Here we summarize the recent advances in research on host cell infection regarding the excystation process, attachment and invasion, survival in the cell, egress and the available data on omics.

A highly divergent 33 kDa Cryptosporidium parvum antigen

Previous studies comparing the genome sequences of Cryptosporidium parvum with Cryptosporidium hominis identified a number of highly divergent genes that might reflect positive selection for host specificity. In the present study, the C. parvum DNA sequence cgd8-5370, which encodes a protein whose amino acid sequence differs appreciably from its homologue in C. hominis , was cloned by PCR and expressed as a recombinant protein in Escherichia coli . Antisera raised against the recombinant cgd8-5370 antigen strongly recognized a unique 33 kDa protein in immunoblots from reducing and non-reducing SDS-PAGE of native C. parvum protein. However, anti-Cp33 sera did not recognize the native 33 kDa homologue in C. hominis . In an immunofluorescence assay (IFA), anti-Cp33 serum recognized an antigen in the anterior end of air-dried C. parvum sporozoites but failed to bind at any sites in C. hominis sporozoites, indicating its specificity for C. parvum . IFA staining of live C. parvum sporozoites with anti-Cp33 serum failed to bind to the parasite, indicating that the CP33 antigen is not on the sporozoite surface, which is consistent with topology predictions based on the encoded amino acid sequence. RT-PCR analysis of cgd8-5370 mRNA before or during C. parvum oocyst excystation revealed transcripts only in excysting sporozoites. Thus, Cp33 represents one of a small number of proteins shown to differentiate C. parvum from C. hominis sporozoites and oocysts.

Amelioration of Cryptosporidium parvum infection in vitro and in vivo by targeting parasite fatty acyl-coenzyme A synthetases

BACKGROUND

Cryptosporidium is emerging as 1 of the 4 leading diarrheal pathogens in children in developing countries. Its infections in patients with AIDS can be fatal, whereas fully effective treatments are unavailable. The major goal of this study is to explore parasite fatty acyl-coenzyme A synthetase (ACS) as a novel drug target.

METHODS

A colorimetric assay was developed to evaluate biochemical features and inhibitory kinetics of Cryptosporidium parvum ACSs using recombinant proteins. Anticryptosporidial efficacies of the ACS inhibitor triacsin C were evaluated both in vitro and in vivo.

RESULTS

Cryptosporidium ACSs displayed substrate preference toward long-chain fatty acids. The activity of parasite ACSs could be specifically inhibited by triacsin C with the inhibition constant Ki in the nanomolar range. Triacsin C was highly effective against C. parvum growth in vitro (median inhibitory concentration, 136 nmol/L). Most importantly, triacsin C effectively reduced parasite oocyst production up to 88.1% with no apparent toxicity when administered to Cryptosporidium-infected interleukin 12 knockout mice at 8-15 mg/kg/d for 1 week.

CONCLUSIONS

The findings of this study not only validated Cryptosporidium ACS (and related acyl-[acyl-carrier-protein]-ligases) as pharmacological targets but also indicate that triacsin C and analogues can be explored as potential new therapeutics against the virtually untreatable cryptosporidial infection in immunocompromised patients.

Metabolomic profiling of faecal extracts from Cryptosporidium parvum infection in experimental mouse models

Cryptosporidiosis is a gastrointestinal disease in humans and animals caused by infection with the protozoan parasite Cryptosporidium. In healthy individuals, the disease manifests mainly as acute self-limiting diarrhoea, but may be chronic and life threatening for those with compromised immune systems. Control and treatment of the disease is challenged by the lack of sensitive diagnostic tools and broad-spectrum chemotherapy. Metabolomics, or metabolite profiling, is an emerging field of study, which enables characterisation of the end products of regulatory processes in a biological system. Analysis of changes in metabolite patterns reflects changes in biochemical regulation, production and control, and may contribute to understanding the effects of Cryptosporidium infection in the host environment. In the present study, metabolomic analysis of faecal samples from experimentally infected mice was carried out to assess metabolite profiles pertaining to the infection. Gas-chromatography mass spectrometry (GC-MS) carried out on faecal samples from a group of C. parvum infected mice and a group of uninfected control mice detected a mean total of 220 compounds. Multivariate analyses showed distinct differences between the profiles of C. parvum infected mice and uninfected control mice,identifying a total of 40 compounds, or metabolites that contributed most to the variance between the two groups. These metabolites consisted of amino acids (n = 17), carbohydrates (n = 8), lipids (n = 7), organic acids (n = 3) and other various metabolites (n = 5), which showed significant differences in levels of metabolite abundance between the infected and uninfected mice groups (p < 0.05). The metabolites detected in this study as well as the differences in abundance between the C. parvum infected and the uninfected control mice, highlights the effects of the infection on intestinal permeability and the fate of the metabolites as a result of nutrient scavenging by the parasite to supplement its streamlined metabolism.

Genome-wide upstream motif analysis of Cryptosporidium parvum genes clustered by expression profile

Background

There are very few molecular genetic tools available to study the apicomplexan parasite Cryptosporidium parvum. The organism is not amenable to continuous in vitro cultivation or transfection, and purification of intracellular developmental stages in sufficient numbers for most downstream molecular applications is difficult and expensive since animal hosts are required. As such, very little is known about gene regulation in C. parvum.

Results

We have clustered whole-genome gene expression profiles generated from a previous study of seven post-infection time points of 3,281 genes to identify genes that show similar expression patterns throughout the first 72 hours of in vitro epithelial cell culture. We used the algorithms MEME, AlignACE and FIRE to identify conserved, overrepresented DNA motifs in the upstream promoter region of genes with similar expression profiles. The most overrepresented motifs were E2F (5′-TGGCGCCA-3′); G-box (5′-G.GGGG-3′); a well-documented ApiAP2 binding motif (5′-TGCAT-3′), and an unknown motif (5′-[A/C] AACTA-3′). We generated a recombinant C. parvum DNA-binding protein domain from a putative ApiAP2 transcription factor [CryptoDB: cgd8_810] and determined its binding specificity using protein-binding microarrays. We demonstrate that cgd8_810 can putatively bind the overrepresented G-box motif, implicating this ApiAP2 in the regulation of many gene clusters.

Conclusion

Several DNA motifs were identified in the upstream sequences of gene clusters that might serve as potential cis-regulatory elements. These motifs, in concert with protein DNA binding site data, establish for the first time the beginnings of a global C. parvum gene regulatory map that will contribute to our understanding of the development of this zoonotic parasite.

Cryptosporidium pathogenicity and virulence

Cryptosporidium is a protozoan parasite of medical and veterinary importance that causes gastroenteritis in a variety of vertebrate hosts. Several studies have reported different degrees of pathogenicity and virulence among Cryptosporidium species and isolates of the same species as well as evidence of variation in host susceptibility to infection. The identification and validation of Cryptosporidium virulence factors have been hindered by the renowned difficulties pertaining to the in vitro culture and genetic manipulation of this parasite. Nevertheless, substantial progress has been made in identifying putative virulence factors for Cryptosporidium. This progress has been accelerated since the publication of the Cryptosporidium parvum and C. hominis genomes, with the characterization of over 25 putative virulence factors identified by using a variety of immunological and molecular techniques and which are proposed to be involved in aspects of host-pathogen interactions from adhesion and locomotion to invasion and proliferation. Progress has also been made in the contribution of host factors that are associated with variations in both the severity and risk of infection. Here we provide a review comprised of the current state of knowledge on Cryptosporidium infectivity, pathogenesis, and transmissibility in light of our contemporary understanding of microbial virulence.

Transcriptome analysis reveals unique metabolic features in the Cryptosporidium parvum Oocysts associated with environmental survival and stresses

Background

Cryptosporidium parvum is a globally distributed zoonotic parasite and an important opportunistic pathogen in immunocompromised patients. Little is known on the metabolic dynamics of the parasite, and study is hampered by the lack of molecular and genetic tools. Here we report the development of the first Agilent microarray for C. parvum (CpArray15K) that covers all predicted ORFs in the parasite genome. Global transcriptome analysis using CpArray15K coupled with real-time qRT-PCR uncovered a number of unique metabolic features in oocysts, the infectious and environmental stage of the parasite.

Results

Oocyst stage parasites were found to be highly active in protein synthesis, based on the high transcript levels of genes associated with ribosome biogenesis, transcription and translation. The proteasome and ubiquitin associated components were also highly active, implying that oocysts might employ protein degradation pathways to recycle amino acids in order to overcome the inability to synthesize amino acids de novo. Energy metabolism in oocysts was featured by the highest level of expression of lactate dehydrogenase (LDH) gene. We also studied parasite responses to UV-irradiation, and observed complex and dynamic regulations of gene expression. Notable changes included increased transcript levels of genes involved in DNA repair and intracellular trafficking. Among the stress-related genes, TCP-1 family members and some thioredoxin-associated genes appear to play more important roles in the recovery of UV-induced damages in the oocysts. Our observations also suggest that UV irradiation of oocysts results in increased activities in cytoskeletal rearrangement and intracellular membrane trafficking.

Conclusions

CpArray15K is the first microarray chip developed for C. parvum, which provides the Cryptosporidium research community a needed tool to study the parasite transcriptome and functional genomics. CpArray15K has been successfully used in profiling the gene expressions in the parasite oocysts as well as their responses to UV-irradiation. These observations shed light on how the parasite oocysts might adapt and respond to the hostile external environment and associated stress such as UV irradiation.

Genomics and population biology of Cryptosporidium species

We describe recent advances in the genomics and population biology of Cryptosporidium parvum and C. hominis, the causative agents of cryptosporidiosis in humans and animals. Many basic aspects of the biology of Cryptosporidium species remain to be investigated and effective drugs to control cryptosporidiosis are not available. Sequencing and annotation of the genome of C. parvum and C. hominis has uncovered unique features of the metabolism of these species. The recently sequenced genome of the gastric species C. muris is providing new insights into the evolution of the genus. Cryptosporidian sequence information has facilitated the identification of polymorphic genetic markers. Genotyping of oocysts excreted by human and animal hosts using such markers has revealed many new species and genotypes, and is leading to a better understanding of the epidemiology of cryptosporidiosis.

PLP-dependent enzymes as potential drug targets for protozoan diseases

The chemical properties of the B(6) vitamers are uniquely suited for wide use as cofactors in essential reactions, such as decarboxylations and transaminations. This review addresses current efforts to explore vitamin B(6) dependent enzymatic reactions as drug targets. Several current targets are described that are found amongst these enzymes. The focus is set on diseases caused by protozoan parasites. Comparison across a range of these organisms allows insight into the distribution of potential targets, many of which may be of interest in the development of broad range anti-protozoan drugs. This article is part of a Special Issue entitled: Pyridoxal Phosphate Enzymology.

The cell biology of cryptosporidium infection

Cryptosporidiosis remains a significant cause of enteric disease worldwide. Basic investigations of host: pathogen interactions have revealed the intricate processes mediating infection. The following summarizes the interactions that mediate infection and the host responses that both permit and ultimately clear the infection.

The apicomplexan plastid and its evolution

Protistan species belonging to the phylum Apicomplexa have a non-photosynthetic secondary plastid-the apicoplast. Although its tiny genome and even the entire nuclear genome has been sequenced for several organisms bearing the organelle, the reason for its existence remains largely obscure. Some of the functions of the apicoplast, including housekeeping ones, are significantly different from those of other plastids, possibly due to the organelle's unique symbiotic origin.

The apicomplexan Cryptosporidium parvum possesses a single mitochondrial-type ferredoxin and ferredoxin:NADP+ reductase system

We have successfully expressed recombinant mitochondrial-type ferredoxin (mtFd) and ferredoxin:NADP(+) reductase (mtFNR) from Cryptosporidium parvum and characterized their biochemical features for the first time for an apicomplexan. Both C. parvum mtFd (CpmtFd) and FNR (CpmtFNR) were obtained and purified as holo-proteins, in which the correct assembly of [2Fe-2S] cluster in Fd and that of FAD in FNR were confirmed and characterized by UV/vis and electron paramagnetic resonance. These proteins were fully functional and CpmtFNR was capable of transferring electrons from NADPH to CpmtFd in a cytochrome c-coupled assay that followed a typical Michaelis-Menten kinetics. Apicomplexan mtFd and mtFNR proteins were evolutionarily divergent from their counterparts in humans and animals and could be explored as potential drug targets in Cryptosporidium and other apicomplexans.

The reductase domain in a Type I fatty acid synthase from the apicomplexan Cryptosporidium parvum: restricted substrate preference towards very long chain fatty acyl thioesters

Background

The apicomplexan Cryptosporidium parvum genome possesses a 25-kb intronless open reading frame (ORF) that predicts a multifunctional Type I fatty acid synthase (CpFAS1) with at least 21 enzymatic domains. Although the architecture of CpFAS1 resembles those of bacterial polyketide synthases (PKSs), this megasynthase is predicted to function as a fatty acyl elongase as our earlier studies have indicated that the N-terminal loading unit (acyl-[ACP] ligase) prefers using intermediate to long chain fatty acids as substrates, and each of the three internal elongation modules contains a complete set of enzymes to produce a saturated fatty acyl chain. Although the activities of almost all domains were confirmed using recombinant proteins, that of the C-terminal reductase domain (CpFAS1-R) was yet undetermined. In fact, there were no published studies to report the kinetic features of any reductase domains in bacterial PKSs using purified recombinant or native proteins.

Results

In the present study, the identity of CpFAS1-R as a reductase is confirmed by in silico analysis on sequence similarity and characteristic motifs. Phylogenetic analysis based on the R-domains supports a previous notion on the bacterial origin of apicomplexan Type I FAS/PKS genes. We also developed a novel assay using fatty acyl-CoAs as substrates, and determined that CpFAS1-R could only utilize very long chain fatty acyl-CoAs as substrates (i.e., with activity on C26 > C24 > C22 > C20, but no activity on C18 and C16). It was capable of using both NADPH and NADH as electron donors, but prefers NADPH to NADH. The activity of CpFAS1-R displayed allosteric kinetics towards C26 hexacosanoyl CoA as a substrate (h = 2.0; V_max = 32.8 nmol min^-1 mg^-1 protein; and K₅₀ = 0.91 mM).

Conclusions

We have confirmed the activity of CpFAS1-R by directly assaying its substrate preference and kinetic parameters, which is for the first time for a Type I FAS, PKS or non-ribosomal peptide synthase (NRPS) reductase domain. The restricted substrate preference towards very long chain fatty acyl thioesters may be an important feature for this megasynthase to avoid the release of product(s) with undesired lengths.

A genome-scale metabolic model of Cryptosporidium hominis

The apicomplexan Cryptosporidium is a protozoan parasite of humans and other mammals. Cryptosporidium species cause acute gastroenteritis and diarrheal disease in healthy humans and animals, and cause life-threatening infection in immunocompromised individuals such as people with AIDS. The parasite has a one-host life cycle and commonly invades intestinal epithelial cells. The current genome annotation of C. hominis, the most serious human pathogen, predicts 3884 genes of which ca. 1581 have predicted functional annotations. Using a combination of bioinformatics analysis, biochemical evidence, and high-throughput data, we have constructed a genome-scale metabolic model of C. hominis. The model is comprised of 213 gene-associated enzymes involved in 540 reactions among the major metabolic pathways and provides a link between the genotype and the phenotype of the organism, making it possible to study and predict behavior based upon genome content. This model was also used to analyze the two life stages of the parasite by integrating the stage-specific proteomic data for oocyst and sporozoite stages. Overall, this model provides a computational framework to systematically study and analyze various functional behaviors of C. hominis with respect to its life cycle and pathogenicity.