Nuclear translocation and accumulation of glyceraldehyde-3-phosphate dehydrogenase involved in diclazuril-induced apoptosis in Eimeria tenella (E. tenella)

Comparative proteomic analysis across the developmental stages of the Eimeria tenella

Eimeria tenella is the main pathogen responsible for coccidiosis in chickens. The life cycle of E. tenella is, arguably, the least complex of all Coccidia, with only one host. However, it presents different developmental stages, either in the environment or in the host and either intracellular or extracellular. Its signaling and metabolic pathways change with its different developmental stages. Until now, little is known about the developmental regulation and transformation mechanisms of its life cycle. In this study, protein profiles from the five developmental stages, including unsporulated oocysts (USO), partially sporulated (7 h) oocysts (SO7h), sporulated oocysts (SO), sporozoites (S) and second-generation merozoites (M2), were harvested using the label-free quantitative proteomics approach. Then the differentially expressed proteins (DEPs) for these stages were identified. A total of 314, 432, 689, and 665 DEPs were identified from the comparison of SO7h vs USO, SO vs SO7h, S vs SO, and M2 vs S, respectively. By conducting weighted gene coexpression network analysis (WGCNA), six modules were dissected. Proteins in blue and brown modules were calculated to be significantly positively correlated with the E. tenella developmental stages of sporozoites (S) and second-generation merozoites (M2), respectively. In addition, hub proteins with high intra-module degree were identified. Gene Ontology (GO) and Kyoto Encyclopedia of Gene and Genomes (KEGG) pathway enrichment analyses revealed that hub proteins in blue modules were involved in electron transport chain and oxidative phosphorylation. Hub proteins in the brown module were involved in RNA splicing. These findings provide new clues and ideas to enhance our fundamental understanding of the molecular mechanisms underlying parasite development.

Diclazuril-induced expression of CDK-related kinase 2 in the second-generation merozoites of Eimeria tenella

Diclazuril is a classic anticoccidial drug. The key molecules of diclazuril in anticoccidial action allows target screening for the development of anticoccidial drugs. Cyclin-dependent kinases (CDK) are prominent target proteins in apicomplexan parasites. In this study, a diclazuril anticoccidiosis animal model was established, and the transcription and translation levels of the CDK-related kinase 2 of Eimeria tenella (EtCRK2) were detected. mRNA and protein expression levels of EtCRK2 decreased in the infected/diclazuril group compared with those in the infected/control group. In addition, immunofluorescence analysis showed that EtCRK2 was localised in the cytoplasm of the merozoites. The fluorescence intensity of EtCRK2 in the infected/diclazuril group was significantly weaker than that in the infected/control group. The anticoccidial drug diclazuril against E.tenella affects the expression pattern of EtCRK2 molecule, and EtCRK2 is a potential target for new drug development.

Comparison of endogenous development, invasion ability and apoptotic features between diclazuril resistant and sensitive strains of Eimeria tenella

Diclazuril (DIC) is widely used in the poultry industry to control coccidiosis. However, drug resistance makes it less effective, and the underlying mechanism remains unclear. One DIC-resistant E. tenella (RE) isolate and one sensitive E. tenella (SE) isolate were used to compare the differences in their endogenous development, pathogenicity, invasion-related gene expression and apoptotic characteristics. Chickens were allocated into four groups to receive RE or SE strain and their corresponding DIC treatment or not. Caeca tissues were sampled at 96 h, 120 h and 144 h post-infection (PI) for pathological analysis. Meanwhile, second-generation merozoites (Mz2) were separated at 120 h PI to detect alterations in mitochondrial membrane potential (MMP), apoptotic rate and caspase-3 activity and mRNA expression of protein phosphatase 5 (PP5), glyceraldehyde 3-phosphate dehydrogenase (GAPDH), actin depolymerizing factor (ADF) and microneme proteins (MICs). Haematoxylin and eosin staining revealed that DIC treatment strictly blocked the development of the SE strain but slightly affected the RE strain. Meanwhile, the number of SE Mz2 and their MMP decreased at the same time the apoptotic rate increased after DIC treatment. Real-time quantitative PCR and caspase-3 activity studies demonstrated that Mz2 from the RE strain had higher mRNA expression of ADF and MICs along with no significant changes in GAPDH and caspase-3 activity under DIC pressure compared to its control; in contrast, the mRNA expression of ADF, MICs and PP5 was markedly suppressed in Mz2 from SE with upregulated caspase-3 activity and GAPDH transcription. In addition, the mRNA expression of GAPDH and PP5 in Mz2 from RE was remarkably higher than that of SE. Taken together, the higher mRNA expression of invasion-related genes and almost unaffected endogenous development provide a better understanding of coccidian resistance to DIC.

Molecular characterization of glyceraldehyde-3-phosphate dehydrogenase from Eimeria tenella

Chicken coccidiosis is an extremely common and lethally epidemic disease caused by Eimeria spp. The control measures of coccidiosis depend mainly on drugs. However, the ensuing drug resistance problem has brought considerable economic loss to the poultry industry. In our previous study, comparative transcriptome analyses of a drug-sensitive (DS) strain and two drug-resistant strains (diclazuril-resistant (DZR) and maduramicin-resistant (MRR) strains) of Eimeria tenella were carried out by transcriptome sequencing. The expression of glyceraldehyde-3-phosphate dehydrogenase of E. tenella (EtGAPDH) was upregulated in the two resistant strains. In this study, we cloned and characterized EtGAPDH. Indirect immunofluorescence localization was used to observe the distribution of EtGAPDH in E. tenella. The results showed that the protein was distributed mainly on the surface of sporozoites and merozoites, and in the cytoplasm of merozoites. qPCR was performed to detect the transcription level of EtGAPDH in the different developmental stages of the E. tenella DS strain. The transcription level of EtGAPDH was significantly higher in second-generation merozoites than in the other three stages. The transcription level of EtGAPDH in the different drug-resistant strains and DS strain of E. tenella was also analyzed by qPCR. The results showed that the transcription level was significantly higher in the two drug-resistant strains (MRR and DZR) than in the DS strain. As the concentration of diclazuril and maduramicin increased, the transcription levels also increased. Western blot results showed that EtGAPDH protein was upregulated in the DZR and MRR strains. Enzyme activity showed that the enzyme activity of EtGAPDH was higher in the two resistant strains than in the DS strain. These results showed that EtGAPDH possess several roles that separate and distinct from its glycolytic function and maybe involved in the development of E. tenella resistance to anticoccidial drugs.

Dual-sensitive chitosan derivative micelles for site-specific drug release in the treatment of chicken coccidiosis

Here, we report a “dual-sensitive” drug delivery platform packaged with anti-coccidia drug diclazuril (DIC) applied in the field of intestinal-targeted administration.

Review of triazine antiprotozoal drugs used in veterinary medicine

Triazines are relatively new antiprotozoal drugs that have successfully controlled coccidiosis and equine protozoal myeloencephalitis. These drugs have favorably treated other protozoal diseases such as neosporosis and toxoplasmosis. In this article, we discuss the pharmacological characteristics of five triazines, toltrazuril, ponazuril, clazuril, diclazuril, and nitromezuril which are used in veterinary medicine to control protozoal diseases which include coccidiosis, equine protozoal myeloencephalitis, neosporosis, and toxoplasmosis.

Molecular characterization and protective efficacy of silent information regulator 2A from Eimeria tenella

Background

Silent information regulator 2 (SIR2) proteins are a family of NAD + -dependent protein deacetylases that are considered potential targets for anti-parasitic agents. In this study, we cloned and characterized SIR2A of the protozoan parasite Eimeria tenella (EtSIR2A) and investigated its protective efficacy as a DNA vaccine.

Methods

The EtSIR2A gene encoding 33.37 kDa protein from E. tenella second-generation merozoites was cloned, and recombinant EtSIR2A protein (rEtSIR2A) was produced in an Escherichia coli expression system. The rEtSIR2A was used to immunize rabbits. Anti-rEtSIR2A antibodies were used to determine the immunolocolization of EtSIR2A in the parasite by immunofluorescence assay (IFA). Transcript and protein expression of EtSIR2A in different development stages of E. tenella were observed by quantitative real-time PCR (qPCR) and western blot (WB) analysis, respectively. The recombinant plasmid pCAGGS-EtSIR2A was constructed and its efficacy against E. tenella infection in chickens was evaluated.

Results

qPCR and WB analysis revealed EtSIR2A expression was developmentally regulated at both the mRNA and protein levels. EtSIR2A mRNA levels were higher in unsporulated oocysts than at other developmental stages, including sporulated oocysts, sporozoites and second-generation merozoites. In contrast, EtSIR2A protein expression levels were highest in second-generation merozoites, moderate in unsporulated oocysts and sporulated oocysts and lowest in sporozoites. Immunostaining with anti-rEtSIR2A antibody indicated that EtSIR2A was mainly located in the cytoplasm of sporozoites and second-generation merozoites, and was strongly expressed during first stage schizogony. Animal-challenge experiments demonstrated that immunization with pCAGGS-EtSIR2A significantly increased average body-weight gain, and decreased mean lesion score and oocyst output in chickens.

Conclusions

These results suggest that EtSIR2A may play an important role in parasite cell survival and may be an effective candidate for the development of new vaccines against E. tenella infection in chickens.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1871-0) contains supplementary material, which is available to authorized users.

Molecular Characterization and Immune Protection of a New Conserved Hypothetical Protein of Eimeria tenella

The genome sequences of Eimeria tenella have been sequenced, but >70% of these genes are currently categorized as having an unknown function or annotated as conserved hypothetical proteins, and few of them have been studied. In the present study, a conserved hypothetical protein gene of E. tenella, designated EtCHP559, was cloned using rapid amplification of cDNA 5'-ends (5'RACE) based on the expressed sequence tag (EST). The 1746-bp full-length cDNA of EtCHP559 contained a 1224-bp open reading frame (ORF) that encoded a 407-amino acid polypeptide with the predicted molecular weight of 46.04 kDa. Real-time quantitative PCR analysis revealed that EtCHP559 was expressed at higher levels in sporozoites than in the other developmental stages (unsporulated oocysts, sporulated oocysts and second generation merozoites). The ORF was inserted into pCold-TF to produce recombinant EtCHP559. Using western blotting, the recombinant protein was successfully recognized by rabbit serum against E. tenella sporozoites. Immunolocalization by using EtCHP559 antibody showed that EtCHP559 was mainly distributed on the parasite surface in free sporozoites and became concentrated in the anterior region after sporozoites were incubated in complete medium. The EtCHP559 became uniformly dispersed in immature and mature schizonts. Inhibition of EtCHP559 function using anti-rEtCHP559 polyclonal antibody reduced the ability of E. tenella sporozoites to invade host cells by >70%. Animal challenge experiments demonstrated that the recombinant EtCHP559 significantly increased the average body weight gain, reduced the oocyst outputs, alleviated cecal lesions of the infected chickens, and resulted in anticoccidial index >160 against E. tenella. These results suggest that EtCHP559 plays an important role in sporozoite invasion and could be an effective candidate for the development of a new vaccine against E. tenella.

Safety evaluation of a triazine compound nitromezuril by assessing bacterial reverse mutation, sperm abnormalities, micronucleus and chromosomal aberration

Nitromezuril (NZL) is a novel triazine compound that exhibits remarkable anticoccidial activity. However, mutagenicity and genotoxicity of NZL have not been evaluated to date. This study evaluated the potential risks of NZL by testing for bacterial reverse mutation (Ames), mouse sperm abnormality (SA), bone marrow micronucleus (MN) and chromosomal aberration (CA). Mice were orally administered with NZL at 385, 192 and 96 mg/kg, corresponding to 0.5 ×, 0.25 × and 0.125 × the LD50 of NZL, respectively. No significant increases in SA and CA were found in mice treated with NZL for 5d and 3d, respectively (P>0.05). NZL at 96-385 mg/kg did not have significant influence on micronucleated polychromatic erythrocyte counts (P>0.05). These results suggest that NZL is not genotoxic. However, Ames test results were positive both with and without the S9 system for Salmonella typhimurium TA98 and TA100, suggesting that NZL may be mutagenic. The mutagenic effects of NZL were different in in vitro and in vivo assays. Further studies should be conducted to confirm the safety of using and developing NZL as a novel anticoccidial drug.

Effect of diclazuril on intestinal morphology and SIgA expression in chicken infected with Eimeria tenella

Secretory immunoglobulin A (SIgA), as a vital actor involving in the mucosal immunity, plays a key role in defending a variety of pathogenic infections, such as bacteria, viruses and parasites. Eimeria tenella is an obligate intracellular apicomplexan parasite contacting with the digestive tract mucosa and specially parasitizes chicken caecum, causing a severe form of coccidiosis. Coccidiosis is currently mainly controlled using chemotherapeutic agents. Diclazuril, a classic coccidiostat, was used widely in the poultry industry. Because of the rising problem of drug resistance, it is therefore crucial to understand the pattern of the SIgA expression in the action of diclazuril against E. tenella. In this study, the intestinal morphology in the caecum was analyzed by haematoxylin-eosin (HE) staining, and the SIgA expression was examined by immunohistochemical technique. At the same time, the duodenum, jejunum and ileum tissues have also been evaluated. HE staining results showed that E. tenella infection caused severe damage characterized by structural disorder, haemorrhage, inflammatory cell infiltration, serous and fibrinous exudation in chicken caecum and invisible damage in the duodenum, jejunum and ileum. With the treatment of diclazuril, the damage in the caecum was alleviated obviously. Immunohistochemical analysis demonstrated that the SIgA level in the infected group was increased in the duodenum (p < 0.05), jejunum and ileum, respectively, but decreased (p < 0.01) in the caecum, compared with the control group. Interestingly, the SIgA level was decreased in the duodenum (p < 0.05), jejunum and ileum but increased (p < 0.05) in the caecum in the infected/diclazuril group in comparison to the infected group. The results showed that diclazuril effectively alleviated the damage in the caecum induced by E. tenella and provided a cure for coccidiosis by improving the immune function in chickens.