Leishmania Parasites Act as a Trojan Horse that Paralyzes the Translation System of Host Macrophages

Aminoacyl tRNA Synthetases: Implications of Structural Biology in Drug Development against Trypanosomatid Parasites

The ensemble of aminoacyl tRNA synthetases is regarded as a key component of the protein translation machinery. With the progressive increase in structure-based studies on tRNA synthetase-ligand complexes, the detailed picture of these enzymes is becoming clear. Having known their critical role in deciphering the genetic code in a living system, they have always been chosen as one of the important targets for development of antimicrobial drugs. Later on, the role of aminoacyl tRNA synthetases (aaRSs) on the survivability of trypanosomatids has also been validated. It became evident through several gene knockout studies that targeting even one of these enzymes affected parasitic growth drastically. Such successful studies have inspired researchers to search for inhibitors that could specifically target trypanosomal aaRSs, and their never-ending efforts have provided fruitful results. Taking all such studies into consideration, these macromolecules of prime importance deserve further investigation for the development of drugs that cure spectrum of infections caused by trypanosomatids. In this review, we have compiled advancements of over a decade that have taken place in the pursuit of devising drugs by using trypanosomatid aaRSs as a major target of interest. Several of these inhibitors work on an exemplary low concentration range without posing any threat to the mammalian cells which is a very critical aspect of the drug discovery process. Advancements have been made in terms of using structural biology as an important tool to analyze the architecture of the trypanosomatids aaRSs and concoction of inhibitors with augmented specificities toward their targets. Some of the inhibitors that have been tested on other parasites successfully but their efficacy has so far not been validated against these trypanosomatids have also been appended.

The host mTOR pathway and parasitic diseases pathogenesis

The mechanistic (or mammalian) target of rapamycin (mTOR) is considered as a critical regulatory enzyme involved in essential signaling pathways affecting cell growth, cell proliferation, protein translation, regulation of cellular metabolism, and cytoskeletal structure. Also, mTOR signaling has crucial roles in cell homeostasis via processes such as autophagy. Autophagy prevents many pathogen infections and is involved on immunosurveillance and pathogenesis. Immune responses and autophagy are therefore key host responses and both are linked by complex mTOR regulatory mechanisms. In recent years, the mTOR pathway has been highlighted in different diseases such as diabetes, cancer, and infectious and parasitic diseases including leishmaniasis, toxoplasmosis, and malaria. The current review underlines the implications of mTOR signals and intricate networks on pathogen infections and the modulation of this master regulator by parasites. Parasitic infections are able to induce dynamic metabolic reprogramming leading to mTOR alterations in spite of many other ways impacting this regulatory network. Accordingly, the identification of parasite effects and interactions over such a complex modulation might reveal novel information regarding the biology of the abovementioned parasites and might allow the development of therapeutic strategies against parasitic diseases. In this sense, the effects of inhibiting the mTOR pathways are also considered in this context in the light of their potential for the prevention and treatment of parasitic diseases.

Transcriptome analysis of goldfish (Carassius auratus) in response to Gyrodactylus kobayashii infection

Gyrodactylid monogeneans are widespread parasites of teleost fishes, and infection with these parasites results in high host morbidity and mortality in aquaculture. To comprehensively elucidate the immune mechanisms against Gyrodactylus kobayashii, the transcriptome profiles of goldfish (Carassius auratus) skin after challenge with G. kobayashii were first investigated using next-generation sequencing. Approximately 21 million clean reads per library were obtained, and the average percentage of these clean reads mapped to the reference genome was 82.25%. A total of 556 differentially expressed genes (DEGs), including 344 upregulated and 212 downregulated genes, were identified, and 380 DEGs were successfully annotated and assigned to 95 signaling pathways in Kyoto Encyclopedia of Genes and Genomes (KEGG). In addition, 14 pathways associated with immune response were identified mainly including mTOR signaling pathway, cytokine-cytokine receptor interaction, intestinal immune network for IgA production, toll-like receptor signaling pathway, and phagosome. Twelve genes were selected and validated using qRT-PCR. A similar trend of these genes between RNA-Seq and qRT-PCR was observed, indicating that RNA-Seq data was reliable. Besides, the ALP activity and NO content in serum were significantly higher in the infected goldfish compared with the non-infected goldfish. In summary, this study provides better understandings of immune defense mechanisms of goldfish against G. kobayashii, which will support future molecular research on gyrodactylids and facilitate the prevention and treatment of gyrodactylosis in aquaculture.

A new level of complexity in parasite-host interaction: The role of extracellular vesicles

Humans and animals have co-existed with parasites in a battle of constant adaptation to one another. It is becoming increasingly clear that extracellular vesicles (EVs) play important roles in this co-existence and pathology. This chapter reviews the current research on EVs released by protozoa, nematodes, trematodes, and cestodes with a special focus on EVs in parasite life cycles. The environmental changes experienced by the parasite during its life cycle is associated with distinct changes in EV release and content. The function of these EV seems to have a significant influence on parasite pathology and survival in the host by concomitantly modulating host immune responses and triggering parasite differentiation. The role of EVs in communication between the parasites and the host adds a new level of complexity in our understanding of parasite biology, which may be a key to further understand the complexity behind host-parasite interactions and communication. This increased understanding can, in turn, open up new avenues for vaccine, diagnostic, and therapeutic development for a wide variety of diseases such as parasite infection, cancers, and immunological disorders.

Modulation of inflammation response to murine cutaneous Leishmaniasis by homeopathic medicines: Antimonium crudum 30cH

Background: Leishmaniasis is a zoonotic disease caused by protozoan parasites of the mononuclear phagocytic system. The modulation activity of these cells can interfere in the host/parasite relationship and influences the prognosis.

Methods: We evaluated the effects of the homeopathic preparation Antimonium crudum 30cH on experimental infection induced by Leishmania (L.) amazonensis. Male Balb/c mice were inoculated with 2 × 106 Leishmania (L.) amazonensis promastigotes into the footpad and, after 48 h (acute phase) or 60 days (chronic phase), cell population of lymphocytes and phagocytes present in the peritoneal washing fluid and spleen were analyzed by flow cytometry and histopathology, with histometry of the subcutaneous primary lesion, local lymph node and spleen. Immunohistochemistry was performed to quantify CD3 (T lymphocyte), CD45RA (B lymphocyte) and CD11b (phagocytes) positive cells.

Results: In treated mice, during the acute phase, there was significant increase of the macroscopic lesion, associated to inflammatory edema, as well increase in the number of free amastigotes and B lymphocytes inside the lesion. Increase of B lymphocytes (predominantly B-2 cells) was also seen in the local lymph node, spleen and peritoneum. In the chronic phase, the inflammatory process in the infection focus was reduced, with reduced phagocyte migration and peritoneal increase of B-1a cells (precursors of B-2 immunoglobulin producers cells) and T CD8+ cells.

Conclusion: The treatment of mice with Antimonium crudum 30cH induced a predominantly B cell pattern of immune response in Leishmania (L.) amazonensis experimental infection, alongside the increase of free amastigote forms number in the infection site. The clinical significance of this study is discussed, further studies are suggested.

Spatiotemporal Uncoupling of MicroRNA-Mediated Translational Repression and Target RNA Degradation Controls MicroRNP Recycling in Mammalian Cells

MicroRNA (miRNA)-mediated repression controls expression of more than half of protein-coding genes in metazoan animals. Translation repression is associated with target mRNA degradation initiated by decapping and deadenylation of the repressed mRNAs. Earlier evidence suggests the endoplasmic reticulum (ER) as the site where microRNPs (miRNPs) interact with their targets before translation repression sets in, but the subcellular location of subsequent degradation of miRNA-repressed messages is largely unidentified. Here, we explore the subcellular distribution of essential components of degradation machineries of miRNA-targeted mRNAs. We have noted that interaction of target mRNAs with AGO2 protein on the ER precedes the relocalization of repressed messages to multivesicular bodies (MVBs). The repressed messages subsequently get deadenylated, lose their interaction with AGO2, and become decapped. Blocking maturation of endosomes to late endosome and MVBs by targeting the endosomal protein HRS uncouples miRNA-mediated translation repression from target RNA degradation. HRS is also targeted by the intracellular parasite Leishmania donovani, which curtails the HRS level in infected cells to prevent uncoupling of mRNA-AGO2 interaction, preventing degradation of translationally repressed messages, and thus stops recycling of miRNPs preengaged in repression.

The role of chemokines and their receptors during protist parasite infections

Protists are a diverse collection of eukaryotic organisms that account for a significant global infection burden. Often, the immune responses mounted against these parasites cause excessive inflammation and therefore pathology in the host. Elucidating the mechanisms of both protective and harmful immune responses is complex, and often relies of the use of animal models. In any immune response, leucocyte trafficking to the site of infection, or inflammation, is paramount, and this involves the production of chemokines, small chemotactic cytokines of approximately 8–10 kDa in size, which bind to specific chemokine receptors to induce leucocyte movement. Herein, the scientific literature investigating the role of chemokines in the propagation of immune responses against key protist infections will be reviewed, focussing onPlasmodiumspecies,Toxoplasma gondii, Leishmaniaspecies andCryptosporidiumspecies. Interestingly, many studies find that chemokines can in fact, promote parasite survival in the host, by drawing in leucocytes for spread and further replication. Recent developments in drug targeting against chemokine receptors highlights the need for further understanding of the role played by these proteins and their receptors in many different diseases.

Suppression of host PTEN gene expression for Leishmania donovani survival in Indian visceral leishmaniasis

Lipid phosphatase, PTEN is amongst the host gene actively involved in determining disease susceptibility. Expression of pten and other genes in vicinity egr1 &4e-bp1 were evaluated in splenic tissue before and after treatment in visceral leishmaniasis patients. Lower expression of egr1 in correlation with pten suppressed 4e-bp1 gene in active cases. The higher levels of pten mRNA expression post treatment confirmed its role in effective clearance of Leishmania. Therefore, it is hypothesized that lower mRNA expression of pten is due to suppression of egr1 activates PI3K signaling bestowing host the ability to cope up infection and continue its normal metabolic machinery.