The effect of autophagy on the survival and invasive activity of Eimeria tenella sporozoites

Pathogenic mechanism of Eimeria tenella autophagy activation of chicken embryo cecal epithelial cells induced by Eimeria tenella

Eimeria tenella mainly invades and develops into cecal epithelial cells of chickens, resulting in cecal epithelial cell damage. Infectious intracellular pathogens possibly act by influencing the autophagy process after invading cells. The interaction between E. tenella and the autophagy of host cells was explored by infecting E. tenella with chick embryo cecal epithelial cells. Transmission electron microscopy, laser confocal microscopy, and Western blot analysis were used to demonstrate that E. tenella infection could induce autophagy in host cells. Results showed that infection with E. tenella induced the formation of autophagosomes in cells. The expression of ATG 5, Beclin-1, and LC3B-II proteins were significantly (P < 0.01) increased after E. tenella infected host cells. Expression of p62 protein levels were significantly (P < 0.01) decreased in host cells infected with E. tenella. Chloroquine (CQ) significantly (P < 0.01) increased the expression levels of LC3B-II and P62 in E. tenella-infected host cells. Rapamycin (RAPA) induced autophagy in host cells, thus reducing the intracellular infection of E. tenella. By contrast, the infection rate of E. tenella increased in cells treated with 3-Methyladenine (3-MA). Hence, E. tenella sporozoite infection could induce autophagy activation in chick embryo cecal epithelial cells, and enhanced autophagy could reduce the infection rate of E. tenella.

Dynamically expressed genes provide candidate viability biomarkers in a model coccidian

Eimeria parasites cause enteric disease in livestock and the closely related Cyclosporacayetanensis causes human disease. Oocysts of these coccidian parasites undergo maturation (sporulation) before becoming infectious. Here, we assessed transcription in maturing oocysts of Eimeria acervulina, a widespread chicken parasite, predicted gene functions, and determined which of these genes also occur in C. cayetanensis. RNA-Sequencing yielded ~2 billion paired-end reads, 92% of which mapped to the E. acervulina genome. The ~6,900 annotated genes underwent temporally-coordinated patterns of gene expression. Fifty-three genes each contributed >1,000 transcripts per million (TPM) throughout the study interval, including cation-transporting ATPases, an oocyst wall protein, a palmitoyltransferase, membrane proteins, and hypothetical proteins. These genes were enriched for 285 gene ontology (GO) terms and 13 genes were ascribed to 17 KEGG pathways, defining housekeeping processes and functions important throughout sporulation. Expression differed in mature and immature oocysts for 40% (2,928) of all genes; of these, nearly two-thirds (1,843) increased their expression over time. Eight genes expressed most in immature oocysts, encoding proteins promoting oocyst maturation and development, were assigned to 37 GO terms and 5 KEGG pathways. Fifty-six genes underwent significant upregulation in mature oocysts, each contributing at least 1,000 TPM. Of these, 40 were annotated by 215 GO assignments and 9 were associated with 18 KEGG pathways, encoding products involved in respiration, carbon fixation, energy utilization, invasion, motility, and stress and detoxification responses. Sporulation orchestrates coordinated changes in the expression of many genes, most especially those governing metabolic activity. Establishing the long-term fate of these transcripts in sporulated oocysts and in senescent and deceased oocysts will further elucidate the biology of coccidian development, and may provide tools to assay infectiousness of parasite cohorts. Moreover, because many of these genes have homologues in C. cayetanensis, they may prove useful as biomarkers for risk.

Identification and Characterization of the ATG8, a Marker of Eimeria tenella Autophagy

Autophagy plays an important role in maintaining cell homeostasis through degradation of denatured proteins and other biological macromolecules. In recent years, many researchers focus on mechanism of autophagy in apicomplexan parasites, but little was known about this process in avian coccidia. In our present study. The cloning, sequencing and characterization of autophagy-related gene (Etatg8) were investigated by quantitative real-time PCR (RT-qPCR), western blotting (WB), indirect immunofluorescence assays (IFAs) and transmission electron microscopy (TEM), respectively. The results have shown 375-bp ORF of Etatg8, encoding a protein of 124 amino acids in E. tenella, the protein structure and properties are similar to other apicomplexan parasites. RT-qPCR revealed Etatg8 gene expression during four developmental stages in E. tenella, but their transcriptional levels were significantly higher at the unsporulated oocysts stage. WB and IFA showed that EtATG8 was lipidated to bind the autophagosome membrane under starvation or rapamycin conditions, and aggregated in the cytoplasm of sporozoites and merozoites, however, the process of autophagosome membrane production can be inhibited by 3-methyladenine. In conclusion, we found that E. tenella has a conserved autophagy mechanism like other apicomplexan parasites, and EtATG8 can be used as a marker for future research on autophagy targeting avian coccidia.

Autophagy induced by monensin serves as a mechanism for programmed death in Eimeria tenella

Monensin (Mon), the first ionophoric antibiotic has widely been used for the treatment and prevention of coccidiosis in poultry until recently, however, at present; its efficacy has been compromised with the emergence of many Mon-resistant strains. Knowledge of the mode of the action of anti-parasitic agents is as important as for other antimicrobials, especially for discovery and long term use of the existing drugs. However, little is known about anti-parasitic drug: monensin's, mechanism of action and physiological alteration in Eimeria tenella. In this study, we explored Mon effects on the viability of Mon-Sensitive GZ (MonS-GZ) and Mon-Resistant GZ (MonR-GZ) Eimeria tenella strains using trypan blue staining and investigated Mon-induced autophagy using Western blotting, indirect immunofluorescence assay, and transmission electron microscopy. The results showed that monensin leads to programmed death of E. tenella parasites by inducing autophagy as a mechanism of anticoccidial action. Mon-induced autophagy was indicated by the decreased sporozoites survival rate, ATG8 over expression and localization, and intracellular vacuolar structures and autophagosomes formation in MonS-GZ strain while in MonR-GZ strains autophagy pathway was not triggered. The autophagy inhibitor 3-methyladenine (3-MA) effectively blocked programmed cell death and saved the MonS-GZ sporozoites. These findings indicated that autophagy serves as a potentially important mechanism of E. tenella cell death in response to Mon and disruption of the autophagy pathway may lead to emergence of drug resistance against this anti-parasitic drug.

Effect of different floatation solutions on E. tenella oocyst purification and optimization of centrifugation conditions for improved recovery of oocysts and sporocysts

Saturated salt floatation method is widely used for coccidian oocyst purification. However, the repeated procedures and inefficient oocysts recovery rate are a continuous challenge. This study aimed to investigate the best suitable floatation solution, along with optimal centrifugation speed and time for Eimeria tenella (E. tenella) oocyst and sporocyst purification. Different floatation solutions i-e, saturated salt, Sheather's sugar and sodium hypochlorite (NaClO) at 20-60% concentrations were used to purify oocyst. It was found that about 96.99% oocysts (8609×g for 10 min) were recovered under these conditions without any effect on the viability of sporocysts. The recovery rate of oocysts using 50% NaClO (V/V) was significantly higher than 35% saturated salt flotation solution (P < 0.05). The optimal method for purification of oocysts based our experimentation was centrifugation at 8609×g for 3 min using 50% NaClO floatation solution, and the optimized centrifugation conditions for improved recovery of sporocysts (about 99.3%) were at 2152×g for 5 min. The present study provided a better method for the coccidian oocyst purification, which could be successfully adopted as a better alternative to existing techniques commonly used for investigations/research pertaining to coccidia.