Theileria's Strategies and Effector Mechanisms for Host Cell Transformation: From Invasion to Immortalization

Theileria parasites sequester host eIF5A to escape elimination by host-mediated autophagy

Intracellular pathogens develop elaborate mechanisms to survive within the hostile environments of host cells. Theileria parasites infect bovine leukocytes and cause devastating diseases in cattle in developing countries. Theileria spp. have evolved sophisticated strategies to hijack host leukocytes, inducing proliferative and invasive phenotypes characteristic of cell transformation. Intracellular Theileria parasites secrete proteins into the host cell and recruit host proteins to induce oncogenic signaling for parasite survival. It is unknown how Theileria parasites evade host cell defense mechanisms, such as autophagy, to survive within host cells. Here, we show that Theileria annulata parasites sequester the host eIF5A protein to their surface to escape elimination by autophagic processes. We identified a small-molecule compound that reduces parasite load by inducing autophagic flux in host leukocytes, thereby uncoupling Theileria parasite survival from host cell survival. We took a chemical genetics approach to show that this compound induced host autophagy mechanisms and the formation of autophagic structures via AMPK activation and the release of the host protein eIF5A which is sequestered at the parasite surface. The sequestration of host eIF5A to the parasite surface offers a strategy to escape elimination by autophagic mechanisms. These results show how intracellular pathogens can avoid host defense mechanisms and identify a new anti-Theileria drug that induces autophagy to target parasite removal.

In vitro infection of bovine erythrocytes with Theileria annulata merozoites as a key step in completing the T. annulata life cycle in vitro

Theileria annulata is a protozoan parasite with a complex life cycle involving a bovine host and a tick vector. It is transmitted by Hyalomma ticks and is the causative agent of tropical theileriosis, a debilitating and often fatal disease in southern Europe, northern Africa and large parts of Asia. Understanding the biology of different life cycle stages is critical for the control of tropical theileriosis and requires the use of experimental animals which poses an ethical concern. We present for the first time the in vitro infection of red blood cells (RBCs) with T. annulata differentiated schizonts. The Ankara cell line of T. annulata was cultured at 41 °C for nine days to induce merogony and subsequently incubated with purified RBCs for one to three days. Percentage of parasitized erythrocyte (PPE) over the short culture period was estimated by Giemsa staining (0.007-0.01%), Flow cytometry activated sorting (FACS) (0.02-1.1%) and observation of FACS sorted cells by confocal microscopy (0.05-0.4%). There was a significant difference in the PPE between FACS and the two other techniques (one-way ANOVA followed by Tukey test, P = 0.004) but no significant difference was observed between the confocal imaging and Giemsa staining methods (ANOVA one-way followed by Tukey test, P = 0.06). Importantly, all three complementary methods confirmed the invasion of RBCs by T. annulata merozoites in vitro. Although the experimental conditions will require further optimization to increase the PPE, the in vitro infection of RBCs by T. annulata merozoites is pivotal in paving the way for the eventual completion of the T. annulata life cycle in vitro when combined with artificial tick feeding.

Guardians of the Herd: Molecular Surveillance of Tick Vectors Uncovers Theileriosis Perils in Large Ruminants

Theileria sp. (Piroplasmida: Theileriidae) is one of the most widely known infections transmitted by hard ticks (Acari: Ixodidae) and has been linked to significant economic losses across the globe. The study's main emphasis was theileriosis, a disease that is common in Pakistan and has an incidence ranging from 0.6% to 33%. Through DNA screening of the vector ticks and host blood, this study sought to determine the risk of tick-borne theileriosis in populations of buffalos (Bubalus bubalis) and cattle (Bos indicus) in Toba Tek Singh district of Punjab, Pakistan. Identified tick species include Hyalomma anatolicum (35.4%), Rhipicephalus (Boophilus) microplus (30.2%), and R. sanguineus (25%). Tick specimens were collected from animals and their respective microenvironments. PCR assays targeting Theileria annulata were used to investigate the infection in the DNA extracted from the collected blood samples from large ruminants and salivary glands (SGs) of the Hyalomma ticks. The 18S rRNA of T. annulata was amplified using specific primers. Positive T. annulata amplicons were sequenced and verified using BLAST analysis. Overall, 50% of SGs contained T. annulate DNA. Female ticks, and those collected from cattle and from riverine environments had significantly higher (p < 0.05) rates of Theileria infection in their acini. Overall prevalence of Theileria infection was 35.9% in blood collected from large ruminants. Cattle had a substantially greater frequency of bovine theileriosis (43.2%) than buffalos (28.7%). Age and sex of large ruminants were significantly positively associated (p < 0.05) with Theileria infection. Furthermore, compared to non-riverine cattle (35%) and buffalo (19.5%), riverine cattle (52.2%) and buffalo (36.2%) showed a considerably higher prevalence. The results of this study, which is the first in Pakistan to examine the blood of large ruminants and vectorial function of Ixodid ticks in the transmission of T. annulata along with associated risk factors, offer an important insight for risk assessment of Theileria infection in livestock using vectorial infectivity.

Growth inhibitory effect of selected quinones from Indian medicinal plants against Theileria annulata

Tropical Bovine Theileriosis, caused by the protozoan parasite Theileria annulata, poses a significant threat to cattle populations. Currently, Buparvaquone is the sole effective naphthoquinone drug commercially available for its treatment. In our research, we delved into the potential of naturally occurring quinones as alternative treatments. We isolated two quinones, emodin and chrysophanol, from Rheum emodi Wall, and two more, embelin and lawsone, from Embelia ribes Burm.f. and Lawsonia inermis L. respectively. We assessed the anti-Theileria efficacy of these quinones in vitro using MTT and flow cytometric assays on T. annulata-infected bovine lymphocytes. Additionally, we evaluated their safety on uninfected bovine Peripheral Blood Mononuclear Cells (PBMC) and Vero cells. Emodin emerged as a promising candidate, exhibiting an IC50 value of 4 μM, surpassing that of buparvaquone. Emodin also displayed relatively low LD50 values of 1.74 mM against uninfected PBMC and 0.87 mM against Vero cells, suggesting potential safety. Remarkably, emodin demonstrated a high cell absorption rate of 71.32%. While emodin's efficacy and bioavailability are encouraging, further research is imperative to validate its safety and effectiveness for treating Tropical Bovine Theileriosis.

Exploring the Transcriptome Dynamics of In Vivo Theileria annulata Infection in Crossbred Cattle

The molecular changes occurring in the host in response to in vivo Theileria annulata parasitic infection are not well understood. Therefore, the present study investigated the differential expression profiles of peripheral blood mononuclear cells (PBMCs) across Theileria annulata-infected and non-infected crossbred cows. The differential expression profiles from PBMCs of infected and non-infected crossbred cows were generated by RNA sequencing. A marked difference in the expression of genes associated with innate immunity (FTH1, ACTB, ISG15) was observed between the two groups. The over-represented pathways in Theileria annulata-infected cows were associated with the immune system and regulation of the mitotic cycle. Enriched genes and pathways in non-infected animals were associated with the maintenance of chromatin integrity and cell structure. The highly connected genes identified in this study form potential candidates for further investigation into host-parasite interactions in cattle. An improved understanding of the transcriptomic dynamics during theileriosis would lead to underpinning molecular level differences related to the health status of cattle.

Artemisinin derivatives induce oxidative stress leading to DNA damage and caspase-mediated apoptosis in Theileria annulata-transformed cells

BACKGROUND

Bovine theileriosis caused by the eukaryotic parasite Theileria annulata is an economically important tick-borne disease. If it is not treated promptly, this lymphoproliferative disease has a significant fatality rate. Buparvaquone (BPQ) is the only chemotherapy-based treatment available right now. However, with the emergence of BPQ resistance on the rise and no backup therapy available, it is critical to identify imperative drugs and new targets against Theileria parasites.

METHODS

Artemisinin and its derivatives artesunate (ARS), artemether (ARM), or dihydroartemisinin (DHART) are the primary defence line against malaria parasites. This study has analysed artemisinin and its derivatives for their anti-Theilerial activity and mechanism of action.

RESULTS

ARS and DHART showed potent activity against the Theileria-infected cells. BPQ in combination with ARS or DHART showed a synergistic effect. The compounds act specifically on the parasitised cells and have minimal cytotoxicity against the uninfected host cells. Treatment with ARS or DHART induces ROS-mediated oxidative DNA damage leading to cell death. Further blocking intracellular ROS by its scavengers antagonised the anti-parasitic activity of the compounds. Increased ROS production induces oxidative stress and DNA damage causing p53 activation followed by caspase-dependent apoptosis in the Theileria-infected cells.

CONCLUSIONS

Our findings give unique insights into the previously unknown molecular pathways underpinning the anti-Theilerial action of artemisinin derivatives, which may aid in formulating new therapies against this deadly parasite. Video abstract.

Trifloxystrobin blocks the growth of Theileria parasites and is a promising drug to treat Buparvaquone resistance

Theileria parasites are responsible for devastating cattle diseases, causing major economic losses across Africa and Asia. Theileria spp. stand apart from other apicomplexa parasites by their ability to transform host leukocytes into immortalized, hyperproliferating, invasive cells that rapidly kill infected animals. The emergence of resistance to the theilericidal drug Buparvaquone raises the need for new anti-Theileria drugs. We developed a microscopy-based screen to reposition drugs from the open-access Medicines for Malaria Venture (MMV) Pathogen Box. We show that Trifloxystrobin (MMV688754) selectively kills lymphocytes or macrophages infected with Theileria annulata or Theileria parva parasites. Trifloxystrobin treatment reduced parasite load in vitro as effectively as Buparvaquone, with similar effects on host gene expression, cell proliferation and cell cycle. Trifloxystrobin also inhibited parasite differentiation to merozoites (merogony). Trifloxystrobin inhibition of parasite survival is independent of the parasite TaPin1 prolyl isomerase pathway. Furthermore, modeling studies predicted that Trifloxystrobin and Buparvaquone could interact distinctly with parasite Cytochrome B and we show that Trifloxystrobin was still effective against Buparvaquone-resistant cells harboring TaCytB mutations. Our study suggests that Trifloxystrobin could provide an effective alternative to Buparvaquone treatment and represents a promising candidate for future drug development against Theileria spp.

Immunopeptidomic Analysis of BoLA-I and BoLA-DR Presented Peptides from Theileria parva Infected Cells

The apicomplexan parasite Theileria parva is the causative agent of East Coast fever, usually a fatal disease for cattle, which is prevalent in large areas of eastern, central, and southern Africa. Protective immunity against T. parva is mediated by CD8+ T cells, with CD4+ T-cells thought to be important in facilitating the full maturation and development of the CD8+ T-cell response. T. parva has a large proteome, with >4000 protein-coding genes, making T-cell antigen identification using conventional screening approaches laborious and expensive. To date, only a limited number of T-cell antigens have been described. Novel approaches for identifying candidate antigens for T. parva are required to replace and/or complement those currently employed. In this study, we report on the use of immunopeptidomics to study the repertoire of T. parva peptides presented by both BoLA-I and BoLA-DR molecules on infected cells. The study reports on peptides identified from the analysis of 13 BoLA-I and 6 BoLA-DR datasets covering a range of different BoLA genotypes. This represents the most comprehensive immunopeptidomic dataset available for any eukaryotic pathogen to date. Examination of the immunopeptidome data suggested the presence of a large number of coprecipitated and non-MHC-binding peptides. As part of the work, a pipeline to curate the datasets to remove these peptides was developed and used to generate a final list of 74 BoLA-I and 15 BoLA-DR-presented peptides. Together, the data demonstrated the utility of immunopeptidomics as a method to identify novel T-cell antigens for T. parva and the importance of careful curation and the application of high-quality immunoinformatics to parse the data generated.

Detection of Theileria orientalis Genotypes from Cattle in Kyrgyzstan

The ikeda and chitose genotypes of Theileria orientalis, which for many years were thought to be benign, cause a disease that results in significant economic losses in the cattle industry. This study was carried out in order to determine the genotypes of T. orientalis in cattle in Kyrgyzstan, and 149 archived DNA samples known to be T. orientalis were analyzed by the PCR amplification of the major piroplasm surface protein (MPSP) gene region. Single-Strand Conformation Polymorphism (SSCP) analysis was performed to uncover the nucleotide changes in the archived DNA samples, and 15 samples showing different band profiles were subjected to sequence analysis. As a result of the sequence analysis, it was seen that the samples belonged to the buffeli and chitose A genotypes. In order to identify mixed genotypes, PCR was performed using primers specific for these genotypes, and buffeli (type 3), chitose (type 1) and buffeli+chitose were found to be positive in 26.2%, 2% and 71.8% of samples, respectively. As a result of this study, we showed the presence of buffeli (type 3) and chitose (type 1) genotypes of T. orientalis in cattle in Kyrgyzstan. Comprehensive epidemiological studies are needed to understand the clinical infections caused by the pathogenic chitose A and to determine the geographical distribution and different genotypes of T. orientalis.

Characterisation of the Theileria orientalis Piroplasm Proteome across Three Common Genotypes

Theileria orientalis is an emerging apicomplexan pathogen of cattle occurring in areas populated by the principal vector tick, Haemaphysalis longicornis. Unlike transforming Theileria spp. that induce cancer-like proliferation of lymphocytes via their schizont stage, T. orientalis destroys host erythrocytes during its piroplasm phase resulting in anaemia. The underlying pathogenic processes of T. orientalis infection are poorly understood; consequently, there are no vaccines for prevention of T. orientalis infection and chemotherapeutic options are limited. To identify antigens expressed during the piroplasm phase of T. orientalis, including those which may be useful targets for future therapeutic development, we examined the proteome across three common genotypes of the parasite (Ikeda, Chitose and Buffeli) using preparations of piroplasms purified from bovine blood. A combination of Triton X-114 extraction, one-dimensional electrophoresis and LC-MS/MS identified a total of 1113 proteins across all genotypes, with less than 3% of these representing host-derived proteins. Just over three quarters of T. orientalis proteins (78%) identified were from the aqueous phase of the TX-114 extraction representing cytosolic proteins, with the remaining 22% from the detergent phase, representing membrane-associated proteins. All enzymes involved in glycolysis were expressed, suggesting that this is the major metabolic pathway used during the T. orientalis piroplasm phase. Proteins involved in binding and breakdown of haemoglobin were also identified, suggesting that T. orientalis uses haemoglobin as a source of amino acids. A number of proteins involved in host cell interaction were also identified which may be suitable targets for the development of chemotherapeutics or vaccines.

Plasmepsin-like Aspartyl Proteases in Babesia

Apicomplexan genomes encode multiple pepsin-family aspartyl proteases (APs) that phylogenetically cluster to six independent clades (A to F). Such diversification has been powered by the function-driven evolution of the ancestral apicomplexan AP gene and is associated with the adaptation of various apicomplexan species to different strategies of host infection and transmission through various invertebrate vectors. To estimate the potential roles of Babesia APs, we performed qRT-PCR-based expressional profiling of Babesia microti APs (BmASP2, 3, 5, 6), which revealed the dynamically changing mRNA levels and indicated the specific roles of individual BmASP isoenzymes throughout the life cycle of this parasite. To expand on the current knowledge on piroplasmid APs, we searched the EuPathDB and NCBI GenBank databases to identify and phylogenetically analyse the complete sets of APs encoded by the genomes of selected Babesia and Theileria species. Our results clearly determine the potential roles of identified APs by their phylogenetic relation to their homologues of known function—Plasmodium falciparum plasmepsins (PfPM I–X) and Toxoplasma gondii aspartyl proteases (TgASP1–7). Due to the analogies with plasmodial plasmepsins, piroplasmid APs represent valuable enzymatic targets that are druggable by small molecule inhibitors—candidate molecules for the yet-missing specific therapy for babesiosis.