A cysteine protease of Babesia microti and its interaction with tick cystatins

Effect of protease inhibitors on the intraerythrocytic development of Babesia microti and Babesia duncani, the causative agents of human babesiosis

Human babesiosis is a malaria-like, tick-borne infectious disease with a global distribution. Babesiosis is caused by intraerythrocytic, apicomplexan parasites of the genus Babesia. In the United States, human babesiosis is caused by Babesia microti and Babesia duncani. Current treatment for babesiosis includes either the combination of atovaquone and azithromycin or the combination of clindamycin and quinine. However, the side effects of these agents and the resistance posed by these parasites call for alternative approaches for treating human babesiosis. Proteases play several roles in the context of parasitic lifestyle and regulate basic biological processes including cell death, cell progression, and cell migration. Using the SYBR Green-1 assay, we screened a protease inhibitor library that consisted of 160 compounds against B. duncani in vitro and identified 13 preliminary hits. Dose response assays of hit compounds against B. duncani and B. microti under in vitro conditions identified five effective inhibitors against parasite growth. Of these compounds, we chose ixazomib, a proteasome inhibitor as a potential drug for animal studies based on its lower IC50 and a higher therapeutic index in comparison with other compounds. Our results suggest that Babesia proteasome may be an important drug target and that developing this class of drugs may be important to combat human babesiosis.

Exploring the longitudinal expression dynamics of midguts in adult female Amblyomma americanum ticks

BACKGROUND

Female ticks remain attached to their host for multiple days to complete a blood meal. This prolonged feeding period is accompanied by a significant increase in the tick's size and body weight, paralleled by noteworthy changes to the tick midgut. While the midgut is recognized for its established role in blood storage and processing, its importance extends to playing a crucial role in the acquisition, survival, and proliferation of pathogens. Despite this, our overall understanding of tick midgut biology is limited.

RESULTS

Our transcriptome analysis identified 15,599 putative DNA coding sequences (CDS), which were classified into 26 functional groups. Dimensional and differential expression analyses revealed four primary transcriptional profiles corresponding to unfed, slow-feeding, transitory (from slow- to rapid-feeding), and rapid-feeding stages. Additionally, comparing the current dataset with previously deposited transcriptome from other tick species allowed the identification of commonly expressed transcripts across different feeding stages.

CONCLUSION

Our findings provide a detailed temporal resolution of numerous metabolic pathways in the midgut of A. americanum adult females throughout the feeding process, highlighting the dynamic transcriptional regulation of the tick's midgut as feeding progresses. Furthermore, we identified conserved transcripts across three different tick species that exhibit similar expression patterns. This knowledge not only enhances our understanding of the physiological processes within the tick midgut but also opens up potential avenues for developing control methods that target multiple tick species.

Exploring midgut expression dynamics: longitudinal transcriptomic analysis of adult female Amblyomma americanum midgut and comparative insights with other hard tick species

Background

Female ticks remain attached to their host for multiple days to complete a blood meal. This prolonged feeding period is accompanied by a significant increase in the tick's size and body weight, paralleled by noteworthy changes to the tick midgut. While the midgut is recognized for its established role in blood storage and processing, its importance extends to playing a crucial role in the acquisition, survival, and proliferation of pathogens. Despite this, our overall understanding of tick midgut biology is limited.

Results

We conducted a comprehensive longitudinal transcriptome analysis of the midgut in adult female A. americanum ticks across various feeding stages, including unfed, slow-feeding, and rapid-feeding phases. Our analysis revealed 15,599 putative DNA coding sequences (CDS) classified within 26 functional groups. Dimensional and differential expression analysis highlighted the dynamic transcriptional changes in the tick midgut as feeding progresses, particularly during the initial period of feeding and the transition from the slow-feeding to the rapid-feeding phase. Additionally, we performed an orthology analysis comparing our dataset with midgut transcriptomes from other hard ticks, such as Ixodes scapularis and Rhipicephalus microplus. This comparison allowed us to identify transcripts commonly expressed during different feeding phases across these three species.

Conclusion

Our findings provide a detailed temporal resolution of numerous metabolic pathways in A. americanum, emphasizing the dynamic transcriptional changes occurring in the tick midgut throughout the feeding process. Furthermore, we identified conserved transcripts across three different tick species that exhibit similar expression patterns. This knowledge has significant implications for future research aimed at deciphering the physiological pathways relevant within the tick midgut. It also offers potential avenues for developing control methods that target multiple tick species.

A longitudinal transcriptomic analysis of Rhipicephalus microplus midgut upon feeding

Rhipicephalus microplus, a highly host-specific tick that primarily feeds on cattle, posing a significant threat to livestock production. The investigation of tick physiology is crucial for identifying potential targets in tick control. Of particular interest adult female ticks undergo a significant expansion of the midgut during feeding, leading to an over 100-fold increase in body weight. Beyond the functions of storing and digesting blood meals, the tick midgut plays a crucial role in acquiring and transmitting pathogens. However, our understanding of tick midgut physiology remains limited. In this study we conducted a comprehensive longitudinal transcriptome analysis of the midgut from adult female R. microplus ticks collected at various feeding stages, providing an overview of the transcriptional modulation in this organ as feeding progress. By employing a de novo assembly approach followed by coding-sequences (CDS) extraction, 60,599 potential CDS were identified. In preparation for functional annotation and differential expression analysis, transcripts that showed an average transcript per million (TPM) ≥ 3 in at least one of the biological conditions were extracted. This selection process resulted in a total of 10,994 CDS, which were categorized into 24 functional classes. Notably, our differential expression analysis revealed three main transcriptional profiles. In the first one, representing the slow-feeding stage, the most abundant functional classes were the "protein synthesis" and "secreted" groups, reflecting the highly active state of the tick midgut. The second profile partially accounts for the rapid-feeding stage, in which a high number of differentially expressed transcripts was observed. Lastly, the third transcriptional profile represents post-detached ticks. Notably the highest number of modulated transcripts was observed up to 48 h post-detachment (hpd), however no major differences was observed up to 168 hpd. Overall, the data presented here offers a temporal insight into tick midgut physiology, contributing to the identification of potential targets for the development of anti-tick control strategies.

Tick innate immune responses to hematophagy and Ehrlichia infection at single-cell resolution

Introduction

Ticks rely on robust cellular and humoral responses to control microbial infection. However, several aspects of the tick's innate immune system remain uncharacterized, most notably that of the immune cells (called hemocytes), which are known to play a significant role in cellular and humoral responses. Despite the importance of hemocytes in regulating microbial infection, our understanding of their basic biology and molecular mechanisms remains limited. Therefore, we believe that a more detailed understanding of the role of hemocytes in the interactions between ticks and tick-borne microbes is crucial to illuminating their function in vector competence and to help identify novel targets for developing new strategies to block tick-borne pathogen transmission.

Methods

This study examined hemocytes from the lone star tick (Amblyomma americanum) at the transcriptomic level using the 10X genomics single-cell RNA sequencing platform to analyze hemocyte populations from unfed, partially blood-fed, and Ehrlichia chaffeensis-infected ticks. The functional role of differentially expressed hemocyte markers in hemocyte proliferation and Ehrlichia dissemination was determined using an RNA interference approach.

Results and discussion

Our data exhibit the identification of fourteen distinct hemocyte populations. Our results uncover seven distinct lineages present in uninfected and Ehrlichia-infected hemocyte clusters. The functional characterization of hemocytin, cystatin, fibronectin, and lipocalin demonstrate their role in hemocyte population changes, proliferation, and Ehrlichia dissemination.

Conclusion

Our results uncover the tick immune responses to Ehrlichia infection and hematophagy at a single-cell resolution. This work opens a new field of tick innate immunobiology to understand the role of hemocytes, particularly in response to prolonged blood-feeding (hematophagy), and tick-microbial interactions.

Comparative Degradome Analysis of the Bovine Piroplasmid Pathogens Babesia bovis and Theileria annulata

Babesia bovis and Theileria annulata are tick-borne hemoprotozoans that impact bovine health and are responsible for considerable fatalities in tropical and subtropical regions around the world. Both pathogens infect the same vertebrate host, are closely related, and contain similar-sized genomes; however, they differ in invertebrate host specificity, absence vs. presence of a schizont stage, erythrocyte invasion mechanism, and transovarial vs. transstadial transmission. Phylogenetic analysis and bidirectional best hit (BBH) identified a similar number of aspartic, metallo, and threonine proteinases and nonproteinase homologs. In contrast, a considerably increased number of S54 serine rhomboid proteinases and S9 nonproteinase homologs were identified in B. bovis, whereas C1A cysteine proteinases and A1 aspartic nonproteinase homologs were found to be expanded in T. annulata. Furthermore, a single proteinase of families S8 (subtilisin-like protein) and C12 (ubiquitin carboxyl-terminal hydrolase), as well as four nonproteinase homologs, one with dual domains M23-M23 and three with S9-S9, were exclusively present in B. bovis. Finally, a pronounced difference in species-specific ancillary domains was observed between both species. We hypothesize that the observed degradome differences represent functional correlates of the dissimilar life history features of B. bovis and T. annulata. The presented improved classification of piroplasmid proteinases will facilitate an informed choice for future in-depth functional studies.

In Silico Survey and Characterization of Babesia microti Functional and Non-Functional Proteases

Human babesiosis caused by the intraerythrocytic apicomplexan Babesia microti is an expanding tick-borne zoonotic disease that may cause severe symptoms and death in elderly or immunocompromised individuals. In light of an increasing resistance of B. microti to drugs, there is a lack of therapeutic alternatives. Species-specific proteases are essential for parasite survival and possible chemotherapeutic targets. However, the repertoire of proteases in B. microti remains poorly investigated. Herein, we employed several combined bioinformatics tools and strategies to organize and identify genes encoding for the full repertoire of proteases in the B. microti genome. We identified 64 active proteases and 25 nonactive protease homologs. These proteases can be classified into cysteine (n = 28), serine (n = 21), threonine (n = 14), asparagine (n = 7), and metallopeptidases (n = 19), which, in turn, are assigned to a total of 38 peptidase families. Comparative studies between the repertoire of B. bovis and B. microti proteases revealed differences among sensu stricto and sensu lato Babesia parasites that reflect their distinct evolutionary history. Overall, this data may help direct future research towards our understanding of the biology and pathogenicity of Babesia parasites and to explore proteases as targets for developing novel therapeutic interventions.