Leishmania-induced inactivation of the macrophage transcription factor AP-1 is mediated by the parasite metalloprotease GP63

GRASP negatively regulates the secretion of the virulence factor gp63 in Leishmania

Metalloprotease-gp63 is a virulence factor secreted by Leishmania. However, secretory pathway in Leishmania is not well defined. Here, we cloned and expressed the GRASP homolog from Leishmania. We found that Leishmania expresses one GRASP homolog of 58 kDa protein (LdGRASP) which localizes in LdRab1- and LPG2-positive Golgi compartment in Leishmania. LdGRASP was found to bind with COPII complex, LdARF1, LdRab1 and LdRab11 indicating its role in ER and Golgi transport in Leishmania. To determine the function of LdGRASP, we generated LdGRASP knockout parasites using CRISPR-Cas9. We found fragmentation of Golgi in Ld:GRASPKO parasites. Our results showed enhanced transport of non-GPI-anchored gp63 to the cell surface leading to higher secretion of this form of gp63 in Ld:GRASPKO parasites in comparison to Ld:WT cells. In contrast, we found that transport of GPI-anchored gp63 to the cell surface is blocked in Ld:GRASPKO parasites and thereby inhibits its secretion. The overexpression of dominant-negative mutant of LdRab1 or LdSar1 in Ld:GRASPKO parasites significantly blocked the secretion of non-GPI-anchored gp63. Interestingly, we found that survival of transgenic parasites overexpressing Ld:GRASP-GFP is significantly compromised in macrophages in comparison to Ld:WT and Ld:GRASPKO parasites. These results demonstrated that LdGRASP differentially regulates Ldgp63 secretory pathway in Leishmania.

Unconventional role of Rab4 in the secretory pathway in Leishmania

Leishmania donovani is an auxotroph for heme. Parasite acquires heme by clathrin-mediated endocytosis of hemoglobin by specific receptor. However, the regulation of receptor recycling pathway is not known in Leishmania. Here, we have cloned, expressed and characterized the Rab4 homologue from L. donovani. We have found that LdRab4 localizes in both early endosomes and Golgi in L. donovani. To understand the role of LdRab4 in L. donovani, we have generated transgenic parasites overexpressing GFP-LdRab4:WT, GFP-LdRab4:Q67L, and GFP-LdRab4:S22N. Our results have shown that overexpression of GFP-LdRab4:Q67L or GFP-LdRab4:S22N does not alter the cell surface localization of hemoglobin receptor in L. donovani. Surprisingly, we have found that overexpression of GFP-LdRab4:S22N significantly blocks the transport of Ldgp63 to the cell surface whereas the trafficking of Ldgp63 is induced to the cell surface in GFP-LdRab4:WT and GFP-LdRab4:Q67L overexpressing parasites. Consequently, we have found significant inhibition of gp63 secretion by GFP-LdRab4:S22N overexpressing parasites whereas secretion of Ldgp63 is enhanced in GFP-LdRab4:WT and GFP-LdRab4:Q67L overexpressing parasites in comparison to untransfected control parasites. Moreover, we have found that survival of transgenic parasites overexpressing GFP-LdRab4:S22N is severely compromised in macrophages in comparison to GFP-LdRab4:WT and GFP-LdRab4:Q67L expressing parasites. These results demonstrated that LdRab4 unconventionally regulates the secretory pathway in L. donovani.

Extracellular Vesicles Released by Leishmania (Leishmania) amazonensis Promastigotes with Distinct Virulence Profile Differently Modulate the Macrophage Functions

Leishmania spp. is the aetiologic agent of leishmaniasis, a disease endemic in several developing countries. The parasite expresses and secretes several virulence factors that subvert the macrophage function and immune response. Extracellular vesicles (EVs) can carry molecules of the parasites that show immunomodulatory effects on macrophage activation and disease progression. In the present work, we detected a significantly higher expression of lpg3 and gp63 genes in Leishmania amazonensis promastigotes recovered after successive experimental infections (IVD-P) compared to those cultured for a long period (LT-P). In addition, we observed a significantly higher percentage of infection and internalized parasites in groups of macrophages infected with IVD-P. Macrophages previously treated with EVs from LT-P showed higher percentages of infection and production of inflammatory cytokines after the parasite challenge compared to the untreated ones. However, macrophages infected with parasites and treated with EVs did not reduce the parasite load. In addition, no synergistic effects were observed in the infected macrophages treated with EVs and reference drugs. In conclusion, parasites cultured for a long period in vitro and recovered from animals' infections, differently affected the macrophage response. Furthermore, EVs produced by these parasites affected the macrophage response in the early infection of these cells.

Comparative characterization of microRNA-71 of Echinococcus granulosus exosomes

Cystic echinococcosis (CE) is a global zoonotic disease caused by Echinococcus granulosus, posing a great threat to human and animal health. MiRNAs are small regulatory noncoding RNA involved in the pathogenesis of parasitic diseases, possibly via exosomes. Egr-miR-71 has been identified as one of the miRNAs in the blood of CE patients, but its secretory characteristics and functions remains unclear. Herein, we studied the secretory and biological activity of exosomal egr-miR-71 and its immunoregulatory functions in sheep peripheral blood mononuclear cells (PBMCs). Our results showed that egr-miR-71 was enriched in the exosome secreted by protoscoleces with biological activity. These egr-miR-71-containing exosomes were easily internalized and then induced the dysregulation of cytokines (IL-10 and TNF-α), nitric oxide (NO) and key components (CD14 and IRF5) in the LPS/TLR4 pathway in the coincubated sheep PBMCs. Similarly, egr-miR-71 overexpression also altered the immune functions but exhibited obvious differences in regulation of the cytokines and key components, preferably inhibiting proinflammatory cytokines (IL-1α, IL-1β and TNF-α). These results demonstrate that exosomal egr-miR-71 is bioactive and capacity of immunomodulation of PBMCs, potentially being involved in immune responses during E. granulosus infection.

Leishmania species: A narrative review on surface proteins with structural aspects involved in host-pathogen interaction

In tropical and subtropical regions of the world, leishmaniasis is endemic and causes a range of clinical symptoms in people, from severe tegumentary forms (such as cutaneous, mucocutaneous, and diffuse leishmaniasis) to lethal visceral forms. The protozoan parasite of the genus Leishmania causes leishmaniasis, which is still a significant public health issue, according to the World Health Organization 2022. The public's worry about the neglected tropical disease is growing as new foci of the illness arise, which are exacerbated by alterations in behavior, changes in the environment, and an enlarged range of sand fly vectors. Leishmania research has advanced significantly during the past three decades in a few different avenues. Despite several studies on Leishmania, many issues, such as illness control, parasite resistance, parasite clearance, etc., remain unresolved. The key virulence variables that play a role in the pathogenicity-host-pathogen relationship of the parasite are comprehensively discussed in this paper. The important Leishmania virulence factors, such as Kinetoplastid Membrane Protein-11 (KMP-11), Leishmanolysin (GP63), Proteophosphoglycan (PPG), Lipophosphoglycan (LPG), Glycosylinositol Phospholipids (GIPL), and others, have an impact on the pathophysiology of the disease and enable the parasite to spread the infection. Leishmania infection may arise from virulence factors; they are treatable with medications or vaccinations more promptly and might greatly shorten the duration of treatment. Additionally, our research sought to present a modeled structure of a few putative virulence factors that might aid in the development of new chemotherapeutic approaches for the treatment of leishmaniasis. The predicted virulence protein's structure is utilized to design novel drugs, therapeutic targets, and immunizations for considerable advantage from a higher understanding of the host immune response.

Degron Pathways and Leishmaniasis: Debating Potential Roles of Leishmania spp. Proteases Activity on Guiding Hosts Immune Response and Their Relevance to the Development of Vaccines

Degrons are short peptide sequences that signalize target sites for protein degradation by proteases. Herein, we bring forth the discussion on degrons present in proteins related to the immune system of Mus musculus that are potential targets for cysteine and serine proteases of Leishmania spp. and their possible roles on host immune regulation by parasites. The Merops database was used to identify protease substrates and proteases sequence motifs, while MAST/MEME Suite was applied to find degron motifs in murine cytokines (IFN-y, IL-4, IL-5, IL-13, IL-17) and transcription factors (NF-kappaB, STAT-1, AP-1, CREB, and BACH2). STRING tool was used to construct an interaction network for the immune factors and SWISS-MODEL server to generate three-dimensional models of proteins. In silico assays confirm the occurrence of degrons in the selected immune response factors. Further analyses were conducted only in those with resolved three-dimensional structures. The predicted interaction network of degron-containing M. musculus proteins shows the possibility that the specific activity of parasite proteases could interfere with the trend of Th1/Th2 immune responses. Data suggest that degrons may play a role in the immune responses in leishmaniases as targets for parasite proteases activity, directing the degradation of specific immune-related factors.

Insights on Host-Parasite Immunomodulation Mediated by Extracellular Vesicles of Cutaneous Leishmania shawi and Leishmania guyanensis

Leishmaniasis is a parasitic disease caused by different species of Leishmania and transmitted through the bite of sand flies vector. Macrophages (MΦ), the target cells of Leishmania parasites, are phagocytes that play a crucial role in the innate immune microbial defense and are antigen-presenting cells driving the activation of the acquired immune response. Exploring parasite-host communication may be key in restraining parasite dissemination in the host. Extracellular vesicles (EVs) constitute a group of heterogenous cell-derived membranous structures, naturally produced by all cells and with immunomodulatory potential over target cells. This study examined the immunogenic potential of EVs shed by L. shawi and L. guyanensis in MΦ activation by analyzing the dynamics of major histocompatibility complex (MHC), innate immune receptors, and cytokine generation. L. shawi and L. guyanensis EVs were incorporated by MΦ and modulated innate immune receptors, indicating that EVs cargo can be recognized by MΦ sensors. Moreover, EVs induced MΦ to generate a mix of pro- and anti-inflammatory cytokines and favored the expression of MHCI molecules, suggesting that EVs antigens can be present to T cells, activating the acquired immune response of the host. Since nano-sized vesicles can be used as vehicles of immune mediators or immunomodulatory drugs, parasitic EVs can be exploited by bioengineering approaches for the development of efficient prophylactic or therapeutic tools for leishmaniasis.

The glycoprotein gp63- a potential pan drug target for developing new antileishmanial agents

Leishmaniasis is a tropical parasitic disease caused by Leishmania spp. They cause several presentations of illness ranging from cutaneous leishmaniasis to visceral leishmaniasis. The current arsenal of drugs to treat leishmaniasis is limited, and drug resistance further impedes the problem. Therefore, it is necessary to revisit the available information to identify an alternative or new target for treatment. The glycoprotein 63 (gp63), is a potential anti-leishmanial target that plays a significant role in host-pathogen interaction and virulence. Many studies are ongoing to develop gp63 inhibitors or use it as a vaccine target. In this review, we will discuss the potential of gp63 as a drug target. This review summarises the studies focusing on gp63 as a drug target and its inhibitors identified using in silico approaches.

Emerging strategies and challenges of molecular therapeutics in antileishmanial drug development

Molecular therapy refers to targeted therapies based on molecules which have been intelligently directed towards specific biomolecular structures and include small molecule drugs, monoclonal antibodies, proteins and peptides, DNA or RNA-based strategies, targeted chemotherapy and nanomedicines. Molecular therapy is emerging as the most effective strategy to combat the present challenges of life-threatening visceral leishmaniasis, where the successful human vaccine is currently unavailable. Moreover, current chemotherapy-based strategies are associated with the issues of ineffective targeting, unavoidable toxicities, invasive therapies, prolonged treatment, high treatment costs and the development of drug-resistant strains. Thus, the rational approach to antileishmanial drug development primarily demands critical exploration and exploitation of biochemical differences between host and parasite biology, immunocharacteristics of parasite homing, and host-parasite interactions at the molecular/cellular level. Following this, the novel technology-based designing and development of host and/or parasite-targeted therapeutics having leishmanicidal and immunomodulatory activity is utmost essential to improve treatment efficacy. Thus, the present review is focused on immunological and molecular checkpoint targets in host-pathogen interaction, and molecular therapeutic prospects for Leishmania intervention, and the challenges ahead.

Leishmania Vesicle-Depleted Exoproteome: What, Why, and How?

Leishmaniasis, a vector-borne parasitic protozoan disease, is among the most important neglected tropical diseases. In the absence of vaccines, disease management is challenging. The available chemotherapy is suboptimal, and there are growing concerns about the emergence of drug resistance. Thus, a better understanding of parasite biology is essential to generate new strategies for disease control. In this context, in vitro parasite exoproteome characterization enabled the identification of proteins involved in parasite survival, pathogenesis, and other biologically relevant processes. After 2005, with the availability of genomic information, these studies became increasingly feasible and revealed the true complexity of the parasite exoproteome. After the discovery of Leishmania extracellular vesicles (EVs), most exoproteome studies shifted to the characterization of EVs. The non-EV portion of the exoproteome, named the vesicle-depleted exoproteome (VDE), has been mostly ignored even if it accounts for a significant portion of the total exoproteome proteins. Herein, we summarize the importance of total exoproteome studies followed by a special emphasis on the available information and the biological relevance of the VDE. Finally, we report on how VDE can be studied and disclose how it might contribute to providing biologically relevant targets for diagnosis, drug, and vaccine development.

Three types of Leishmania mexicana amastigotes: Proteome comparison by quantitative proteomic analysis

Leishmania is the unicellular parasite transmitted by phlebotomine sand fly bite. It exists in two different forms; extracellular promastigotes, occurring in the gut of sand flies, and intracellular, round-shaped amastigotes residing mainly in vertebrate macrophages. As amastigotes originating from infected animals are often present in insufficient quality and quantity, two alternative types of amastigotes were introduced for laboratory experiments: axenic amastigotes and amastigotes from macrophages infected in vitro. Nevertheless, there is very little information about the degree of similarity/difference among these three types of amastigotes on proteomic level, whose comparison is crucial for assessing the suitability of using alternative types of amastigotes in experiments. In this study, L. mexicana amastigotes obtained from lesion of infected BALB/c mice were proteomically compared with alternatively cultivated amastigotes (axenic and macrophage-derived ones). Amastigotes of all three types were isolated, individually treated and analysed by LC-MS/MS proteomic analysis with quantification using TMT10-plex isobaric labeling. Significant differences were observed in the abundance of metabolic enzymes, virulence factors and proteins involved in translation and condensation of DNA. The most pronounced differences were observed between axenic amastigotes and lesion-derived amastigotes, macrophage-derived amastigotes were mostly intermediate between axenic and lesion-derived ones.

Intracellular pathogen Leishmania intervenes in iron loading into ferritin by cleaving chaperones in host macrophages as an iron acquisition strategy

Iron (Fe) sequestration is one of the most important strategies of the host to control the growth and survival of invading pathogens. Ferritin (Ft) plays a pivotal role in the sequestration mechanism of mammalian hosts by storing Fe. Recent evidence suggests that poly(rC)-binding proteins (PCBPs) act as chaperones for loading Fe into Ft. Incidentally, modulation of host PCBPs in respect to storing Fe in Ft during any infection remains unexplored. Among PCBPs, PCBP1 and PCBP2 are present in every cell type and involved in interacting with Ft for Fe loading. Leishmania donovani (LD) resides within macrophages during the mammalian stage of infection, causing life-threatening visceral leishmaniasis. Here, we reveal the ability of LD to cleave PCBP1 and PCBP2 in host monocytes/macrophages. LD cleaves PCBP1-FLAG into two fragments and PCBP2-FLAG into multiple fragments, thus affecting their interactions with Ft and resulting in decreased Fe loading into Ft. LD-derived culture supernatant or exosome-enriched fractions are also able to cleave PCBPs, suggesting involvement of a secreted protease of the parasite. Using an immune-depletion experiment and transgenic mutants, we confirmed the involvement of zinc-metalloprotease GP63 in cleaving PCBPs. We further revealed that by cleaving host PCBPs, Leishmania could inhibit Fe loading into Ft to accumulate available Fe for higher intracellular growth. This is the first report of a novel strategy adopted by a mammalian pathogen to interfere with Fe sequestration into Ft by cleaving chaperones for its survival advantage within the host.

A Novel Role of Secretory Cytosolic Tryparedoxin Peroxidase in Delaying Apoptosis of Leishmania-Infected Macrophages

The cytosolic tryparedoxin peroxidase (cTXNPx) of Leishmania donovani is a defensive enzyme. Apart from the nonsecretory form, the cTXNPx is released in the spent media of Leishmania cultures and also in the host cell cytosol. The secretory form of the enzyme from the parasite interacts with multiple proteins in the host cell cytosol, the apoptosis-inducing factor (AIF) being one of them. Immunoprecipitation with anti-cTXNPx and anti-AIF antibodies suggests a strong interaction between AIF and cTXNPx. Consequent to parasite invasion, the migration of AIF to the nucleus to precipitate apoptosis is inhibited in the presence of recombinant cTXNPx expressed in the host cell. This inhibition of AIF movement results in lesser host cell death, giving an advantage to the parasite for continued survival. Staurosporine-induced AIF migration to the nucleus was also inhibited in the presence of recombinant cTXNPx in the host cell. Therefore, this study demonstrates the ability of a Leishmania parasite enzyme, cTXNPx, to interfere with the migration of the host AIF protein, providing a survival advantage to the Leishmania parasite.

Revisiting Leishmania GP63 host cell targets reveals a limited spectrum of substrates

Colonization of host phagocytic cells by Leishmania metacyclic promastigotes involves several parasite effectors, including the zinc-dependent metalloprotease GP63. The major mode of action of this virulence factor entails the cleavage/degradation of host cell proteins. Given the potent proteolytic activity of GP63, identification of its substrates requires the adequate preparation of cell lysates to prevent artefactual degradation during cell processing. In the present study, we re-examined the cleavage/degradation of reported GP63 substrates when GP63 activity was efficiently neutralized during the preparation of cell lysates. To this end, we infected bone marrow-derived macrophages with either wild type, Δgp63, and Δgp63+GP63 L. major metacyclic promastigotes for various time points. We prepared cell lysates in the absence or presence of the zinc-metalloprotease inhibitor 1,10-phenanthroline and examined the levels and integrity of ten previously reported host cell GP63 substrates. Inhibition of GP63 activity with 1,10-phenanthroline during the processing of macrophages prevented the cleavage/degradation of several previously described GP63 targets, including PTP-PEST, mTOR, p65RelA, c-Jun, VAMP3, and NLRP3. Conversely, we confirmed that SHP-1, Synaptotagmin XI, VAMP8, and Syntaxin-5 are bona fide GP63 substrates. These results point to the importance of efficiently inhibiting GP63 activity during the preparation of Leishmania-infected host cell lysates. In addition, our results indicate that the role of GP63 in Leishmania pathogenesis must be re-evaluated.

Identification of natural cytochalasins as leads for neglected tropical diseases drug discovery

Investigating the chemical diversity of natural products from tropical environments is an inspiring approach to developing new drug candidates for neglected tropical diseases (NTDs). In the present study, phenotypic screenings for antiprotozoal activity and a combination of computational and biological approaches enabled the identification and characterization of four cytochalasins, which are fungal metabolites from Brazilian biodiversity sources. Cytochalasins A-D exhibited IC50 values ranging from 2 to 20 μM against intracellular Trypanosoma cruzi and Leishmania infantum amastigotes, values comparable to those of the standard drugs benznidazole and miltefosine for Chagas disease and leishmaniasis, respectively. Furthermore, cytochalasins A-D reduced L. infantum infections by more than 80% in THP-1 cells, most likely due to the inhibition of phagocytosis by interactions with actin. Molecular modelling studies have provided useful insights into the mechanism of action of this class of compounds. Furthermore, cytochalasins A-D showed moderate cytotoxicity against normal cell lines (HFF-1, THP-1, and HepG2) and a good overall profile for oral bioavailability assessed in vitro. The results of this study support the use of natural products from Brazilian biodiversity sources to find potential drug candidates for two of the most important NTDs.

Leishmania amazonensis sabotages host cell SUMOylation for intracellular survival

Leishmania parasites use elaborate virulence mechanisms to invade and thrive in macrophages. These virulence mechanisms inhibit host cell defense responses and generate a specialized replicative niche, the parasitophorous vacuole. In this work, we performed a genome-wide RNAi screen in Drosophila macrophage-like cells to identify the host factors necessary for Leishmania amazonensis infection. This screen identified 52 conserved genes required specifically for parasite entry, including several components of the SUMOylation machinery. Further studies in mammalian macrophages found that L. amazonensis infection inhibited SUMOylation within infected macrophages and this inhibition enhanced parasitophorous vacuole growth and parasite proliferation through modulation of multiple genes especially ATP6V0D2, which in turn affects CD36 expression and cholesterol levels. Together, these data suggest that parasites actively sabotage host SUMOylation and alter host transcription to improve their intracellular niche and enhance their replication.

Leishmania intercepts IFN-γR signaling at multiple levels in macrophages

IFN-γ, a type 2 interferon and a cytokine, is critical for both innate and adaptive immunity. IFN-γ binds to the IFN-γRs on the cell membrane of macrophages, signals through JAK1-STAT-1 pathway and induces IFN-γ-stimulated genes (ISGs). As Leishmania amastigotes reside and replicate within macrophages, IFN-γ mediated macrophage activation eventuate in Leishmania elimination. As befits the principle of parasitism, the impaired IFN-γ responsiveness in macrophages ensures Leishmania survival. IFN-γ responsiveness is a function of integrated molecular events at multiple levels in the cells that express IFN-γ receptors. In Leishmania-infected macrophages, reduced IFN-γRα expression, impaired IFN-γRα and IFN-γRβ hetero-dimerization due to altered membrane lipid composition, reduced JAK-1 and STAT-1 phosphorylation but increased STAT-1 degradation and impaired ISGs induction collectively determine the IFN-γ responsiveness and the efficacy of IFN-γ induced antileishmanial function of macrophages. Therefore, parasite load is not only decided by the levels of IFN-γ produced but also by the IFN-γ responsiveness. Indeed, in Leishmania-infected patients, IFN-γ is produced but IFN-γ signalling is downregulated. However, the molecular mechanisms of IFN-γ responsiveness remain unclear. Therefore, we review the current understanding of IFN-γ responsiveness of Leishmania-infected macrophages.

Isolation, characterization, and functional study of extracellular vesicles derived from Leishmania tarentolae

Leishmania (L.) species are protozoan parasites with a complex life cycle consisting of a number of developmental forms that alternate between the sand fly vector and their host. The non-pathogenic species L. tarentolae is not able to induce an active infection in a human host. It has been observed that, in pathogenic species, extracellular vesicles (EVs) could exacerbate the infection. However, so far, there is no report on the identification, isolation, and characterization of L. tarentolae EVs. In this study, we have isolated and characterized EVs from L. tarentolaeGFP+ (tEVs) along with L. majorGFP+ as a reference and positive control. The EVs secreted by these two species demonstrated similar particle size distribution (approximately 200 nm) in scanning electron microscopy and nanoparticle tracking analysis. Moreover, the said EVs showed similar protein content, and GFP and GP63 proteins were detected in both using dot blot analysis. Furthermore, we could detect Leishmania-derived GP63 protein in THP-1 cells treated with tEVs. Interestingly, we observed a significant increase in the production of IFN-γ, TNF-α, and IL-1β, while there were no significant differences in IL-6 levels in THP-1 cells treated with tEVs following an infection with L. major compared with another group of macrophages that were treated with L. major EVs prior to the infection. Another exciting observation of this study was a significant decrease in parasite load in tEV-treated Leishmania-infected macrophages. In addition, in comparison with another group of Leishmania-infected macrophages which was not exposed to any EVs, tEV managed to increase IFN-γ and decrease IL-6 and the parasite burden. In conclusion, we report for the first time that L. tarentolae can release EVs and provide evidence that tEVs are able to control the infection in human macrophages, making them a great potential platform for drug delivery, at least for parasitic infections.

Virulence factors of Leishmania parasite: Their paramount importance in unraveling novel vaccine candidates and therapeutic targets

Leishmaniasis is a neglected tropical disease and remains a global concern for healthcare. It is caused by an opportunistic protozoan parasite belonging to the genus Leishmania and affects millions worldwide. This disease is mainly prevalent in tropical and subtropical regions and is associated with a high risk of public morbidity and mortality if left untreated. Transmission of this deadly disease is aggravated by the bite of female sand-fly vectors (Phlebotomus and Lutzomyia). With time, significant advancement in leishmaniasis-related research has been carried out to cope with the disease burden. Still, the Leishmania parasite has also co-evolved with its host and adapted successfully within the host's lethal milieu/environment. Thus, understanding and knowledge of various leishmanial virulence factors responsible for the parasitic infection are essential for exploring drug targets and vaccine candidates. The present review elucidates the importance of virulence factors in pathogenesis and summarizes the major leishmanial virulence molecules contributing to the parasitic infection during host-pathogen interaction. Furthermore, we have also elaborated on the potential contribution of leishmanial virulence proteins in developing vaccine candidates and exploring novel therapeutics against this parasitic disease. We aim to represent a clearer picture of parasite pathogenesis within the human host that can further aid in unraveling new strategies to fight against the deadly infection of leishmaniasis.

Expression Profile of Genes Related to the Th17 Pathway in Macrophages Infected by Leishmania major and Leishmania amazonensis: The Use of Gene Regulatory Networks in Modeling This Pathway

Leishmania amazonensis and Leishmania major are the causative agents of cutaneous and mucocutaneous diseases. The infections‘ outcome depends on host–parasite interactions and Th1/Th2 response, and in cutaneous form, regulation of Th17 cytokines has been reported to maintain inflammation in lesions. Despite that, the Th17 regulatory scenario remains unclear. With the aim to gain a better understanding of the transcription factors (TFs) and genes involved in Th17 induction, in this study, the role of inducing factors of the Th17 pathway in Leishmania–macrophage infection was addressed through computational modeling of gene regulatory networks (GRNs). The Th17 GRN modeling integrated experimentally validated data available in the literature and gene expression data from a time-series RNA-seq experiment (4, 24, 48, and 72 h post-infection). The generated model comprises a total of 10 TFs, 22 coding genes, and 16 cytokines related to the Th17 immune modulation. Addressing the Th17 induction in infected and uninfected macrophages, an increase of 2- to 3-fold in 4–24 h was observed in the former. However, there was a decrease in basal levels at 48–72 h for both groups. In order to evaluate the possible outcomes triggered by GRN component modulation in the Th17 pathway. The generated GRN models promoted an integrative and dynamic view of Leishmania–macrophage interaction over time that extends beyond the analysis of single-gene expression.

The Pathogenicity and Virulence of Leishmania - interplay of virulence factors with host defenses

Leishmaniasis is a group of disease caused by the intracellular protozoan parasite of the genus Leishmania. Infection by different species of Leishmania results in various host immune responses, which usually lead to parasite clearance and may also contribute to pathogenesis and, hence, increasing the complexity of the disease. Interestingly, the parasite tends to reside within the unfriendly environment of the macrophages and has evolved various survival strategies to evade or modulate host immune defense. This can be attributed to the array of virulence factors of the vicious parasite, which target important host functioning and machineries. This review encompasses a holistic overview of leishmanial virulence factors, their role in assisting parasite-mediated evasion of host defense weaponries, and modulating epigenetic landscapes of host immune regulatory genes. Furthermore, the review also discusses the diagnostic potential of various leishmanial virulence factors and the advent of immunomodulators as futuristic antileishmanial drug therapy.

Leishmania Exosomes/Extracellular Vesicles Containing GP63 Are Essential for Enhance Cutaneous Leishmaniasis Development Upon Co-Inoculation of Leishmania amazonensis and Its Exosomes

Protozoan parasites of the genus Leishmania are transmitted by the bite of infected sand flies leading to a wide range of diseases called leishmaniasis. Recently, we demonstrated that Leishmania spp.-derived exosomes/extracellular vesicles (EVs/LeishEXO) were released in the lumen of the sand fly midgut and to be co-egested with the parasite during the blood meal and that LeishEXO were found to stimulate an inflammatory response conducting to an exacerbated cutaneous leishmaniasis, also it was shown that these vesicles cargo important virulence factors like GP63. Thus, this study aimed to confirm through morphological and proteomic analysis a novel model specificity utilizing another set of GP63-altered Leishmania amazonensis parasite strains. Consequently, we proposed to further study the impact of different GP63 vesicle expression levels on their ability to modulate innate inflammatory cell responses, and finally to determine the importance of GP63 vesicle content on the exacerbation of the cutaneous Leishmania spp. pathology after their host co-inoculation. Our results revealed that the protein composition of extracted extracellular vesicles were similar to each other and that GP63 was the sole virulence factor changed in the exosomes composition confirming the specificity of the chosen novel model. We further demonstrated that vesicles with different GP63 EVs cargo displayed distinctive macrophage immunomodulatory capabilities at both gene and protein expression in vitro. Finally, we showed their diverse impact on the Leishmania spp. cutaneous pathology in an in vivo setting and confirmed GP63 as a primordial component of the ability of these EVs in augmenting the inflammatory cutaneous response in Leishmania spp. infection. Our findings provide new insight on the immune response happening in cutaneous leishmaniasis, shade light on the mechanism behind the host-pathogen interaction occurring in the initial moments of infection, thus creating the opportunity of using them as the target of new pharmacological treatments and vaccinations.

Differential translational regulation of host exosomal proteins play key role in immunomodulation in antimony resistance in Visceral Leishmaniasis: A proteomic profiling study

In host-pathogen interactions, exosomal secretions are crucial for cell to cell communication and have an established role in immunomodulation. Protozoans, including Leishmania, modulates their host vesicular secretions for better survival; although the role of exosomal secretions in unresponsive against sodium antimony gluconate (SAG) has never been documented. In this study, the exosomal proteome of RAW macrophages infected with either SAG responsive (SAG^S) or SAG unresponsive (SAG^R) L. donovani parasites has been compared with uninfected RAW macrophages. Proteins isolated from exosomes were labelled with iTRAQ reagents; followed by subsequent LC-TOF/-MS analysis. In total, 394 proteins (p < 0.05) were identified which were shared common among all sets. Highly differentially expressed proteins were sorted by log2 value -1 and +1 as down regulated and up regulated respectively which yielded 58 proteins in SAG^R and 41 proteins during SAG^S infection. Out of the 58 proteins identified during SAG^R infection, 17 proteins were of immune modulatory function. Network visualization model and pathway analysis revealed the interactions among these proteins via different immunological pathways with reported involvement of some proteins in SAG resistance and host immune modulation. Hence, the differential abundance of immune pathway related proteins in exosomes of infected host during SAG^R infection supports the immune modulatory strategy adopted by SAG resistant parasites for enhanced survival .

Network-Based Approaches Reveal Potential Therapeutic Targets for Host-Directed Antileishmanial Therapy Driving Drug Repurposing

Leishmania parasites are the causal agent of leishmaniasis, an endemic disease in more than 90 countries worldwide. Over the years, traditional approaches focused on the parasite when developing treatments against leishmaniasis. Despite numerous attempts, there is not yet a universal treatment, and those available have allowed for the appearance of resistance. Here, we propose and follow a host-directed approach that aims to overcome the current lack of treatment. Our approach identifies potential therapeutic targets in the host cell and proposes known drug interactions aiming to improve the immune response and to block the host machinery necessary for the survival of the parasite. We started analyzing transcription factor regulatory networks of macrophages infected with Leishmania major. Next, based on the regulatory dynamics of the infection and available gene expression profiles, we selected potential therapeutic target proteins. The function of these proteins was then analyzed following a multilayered network scheme in which we combined information on metabolic pathways with known drugs that have a direct connection with the activity carried out by these proteins. Using our approach, we were able to identify five host protein-coding gene products that are potential therapeutic targets for treating leishmaniasis. Moreover, from the 11 drugs known to interact with the function performed by these proteins, 3 have already been tested against this parasite, verifying in this way our novel methodology. More importantly, the remaining eight drugs previously employed to treat other diseases, remain as promising yet-untested antileishmanial therapies. IMPORTANCE This work opens a new path to fight parasites by targeting host molecular functions by repurposing available and approved drugs. We created a novel approach to identify key proteins involved in any biological process by combining gene regulatory networks and expression profiles. Once proteins have been selected, our approach employs a multilayered network methodology that relates proteins to functions to drugs that alter these functions. By applying our novel approach to macrophages during the Leishmania infection process, we both validated our work and found eight drugs already approved for use in humans that to the best of our knowledge were never employed to treat leishmaniasis, rendering our work as a new tool in the box available to the scientific community fighting parasites.

Going ballistic: Leishmania nuclear subversion of host cell plasticity

Intracellular parasites have evolved intricate strategies to subvert host cell functions for their own survival. These strategies are particularly damaging to the host if the infection involves immune cells, as illustrated by protozoan parasites of the genus Leishmania that thrive inside mononuclear phagocytic cells, causing devastating immunopathologies. While the impact of Leishmania infection on host cell phenotype and functions has been well documented, the regulatory mechanisms underlying host cell subversion were only recently investigated. Here we summarize the current knowledge on how Leishmania infection affects host nuclear activities and propose thought-provoking new concepts on the reciprocal relationship between epigenetic and transcriptional regulation in host cell phenotypic plasticity, its potential subversion by the intracellular parasite, and its relevance for host-directed therapy.

Sandfly Fever Sicilian Virus-Leishmania major co-infection modulates innate inflammatory response favoring myeloid cell infections and skin hyperinflammation

BACKGROUND

The leishmaniases are a group of sandfly-transmitted diseases caused by species of the protozoan parasite, Leishmania. With an annual incidence of 1 million cases, 1 billion people living in Leishmania-endemic regions, and nearly 30,000 deaths each year, leishmaniasis is a major global public health concern. While phlebotomine sandflies are well-known as vectors of Leishmania, they are also the vectors of various phleboviruses, including Sandfly Fever Sicilian Virus (SFSV). Cutaneous leishmaniasis (CL), caused by Leishmania major (L. major), among other species, results in development of skin lesions on the infected host. Importantly, there exists much variation in the clinical manifestation between individuals. We propose that phleboviruses, vectored by and found in the same sandfly guts as Leishmania, may be a factor in determining CL severity. It was reported by our group that Leishmania exosomes are released into the gut of the sandfly vector and co-inoculated during blood meals, where they exacerbate CL skin lesions. We hypothesized that, when taking a blood meal, the sandfly vector infects the host with Leishmania parasites and exosomes as well as phleboviruses, and that this viral co-infection results in a modulation of leishmaniasis.

METHODOLOGY/PRINCIPAL FINDINGS

In vitro, we observed modulation by SFSV in MAP kinase signaling as well as in the IRF3 pathway that resulted in a pro-inflammatory phenotype. Additionally, we found that SFSV and L. major co-infection resulted in an exacerbation of leishmaniasis in vivo, and by using endosomal (Toll-like receptor) TLR3, and MAVS knock-out mice, deduced that SFSV's hyperinflammatory effect was TLR3- and MAVS-dependent. Critically, we observed that L. major and SFSV co-infected C57BL/6 mice demonstrated significantly higher parasite burden than mice solely infected with L. major. Furthermore, viral presence increased leukocyte influx in vivo. This influx was accompanied by elevated total extracellular vesicle numbers. Interestingly, L. major displayed higher infectiveness with coincident phleboviral infection compared to L. major infection alone.

CONCLUSION/SIGNIFICANCE

Overall our work represents novel findings that contribute towards understanding the causal mechanisms governing cutaneous leishmaniasis pathology. Better comprehension of the potential role of viral co-infection could lead to treatment regimens with enhanced effectiveness.

Extracellular vesicles and leishmaniasis: Current knowledge and promising avenues for future development

Extracellular vesicles (EVs) are small, membrane-bound "delivery trucks" that are present in the extracellular environment, including biological fluids. EVs are capable of inducing changes in the physiological status of neighboring cells through the transfer of key macromolecules, and are thought to play a role in a number of pathological processes. Leishmaniasis, caused by the protozoan parasite Leishmania, is an important example. The biology of Leishmania EVs has been studied in detail, and findings point to their role in exacerbation of disease and potential involvement in the perpetuation of drug resistance. Furthermore, the use of EVs for development of vaccines has been explored, as well as their potential use in a number of fields as biomarkers of disease and drug resistance. Here we discuss the latest findings on EVs, with a particular focus on Leishmania, as well as potential avenues for their future development and clinical applications.

Distinct features of the Leishmania cap-binding protein LeishIF4E2 revealed by CRISPR-Cas9 mediated hemizygous deletion

Leishmania parasites cycle between sand-fly vectors and mammalian hosts adapting to alternating environments by stage-differentiation accompanied by changes in the proteome profiles. Translation regulation plays a central role in driving the differential program of gene expression since control of gene regulation in Leishmania is mostly post-transcriptional. The Leishmania genome encodes six eIF4E paralogs, some of which bind a dedicated eIF4G candidate, and each eIF4E is assumed to have specific functions with perhaps some overlaps. However, LeishIF4E2 does not bind any known eIF4G ortholog and was previously shown to comigrate with the polysomal fractions of sucrose gradients in contrast to the other initiation factors that usually comigrate with pre-initiation and initiation complexes. Here we deleted one of the two LeishIF4E2 gene copies using the CRISPR-Cas9 methodology. The deletion caused severe alterations in the morphology of the mutant cells that became round, small, and equipped with a very short flagellum that did not protrude from its pocket. Reduced expression of LeishIF4E2 had no global effect on translation and growth, unlike other LeishIF4Es; however, there was a change in the proteome profile of the LeishIF4E2(+/-) cells. Upregulated proteins were related mainly to general metabolic processes including enzymes involved in fatty acid metabolism, DNA repair and replication, signaling, and cellular motor activity. The downregulated proteins included flagellar rod and cytoskeletal proteins, as well as surface antigens involved in virulence. Moreover, the LeishIF4E2(+/-) cells were impaired in their ability to infect cultured macrophages. Overall, LeishIF4E2 does not behave like a general translation factor and its function remains elusive. Our results also suggest that the individual LeishIF4Es perform unique functions.

Leishmania parasites cause a broad spectrum of diseases with different pathological symptoms. During their life cycle the parasites shuffle between sand-fly vectors and mammalian hosts adapting to the changing environments via a stage specific program of gene expression that promotes their survival. Translation initiation plays a key role in control of gene expression and in Leishmania this is exemplified by the presence of multiple cap-binding complexes that interact with mRNAs. The parasites encode multiple paralogs of the cap-binding translation initiation factor eIF4E and of its corresponding binding partner eIF4G forming complexes with different potential functions. The role of LeishIF4E2 remains elusive: it does not bind any of the LeishIF4G candidate subunits and associates with polysomes, a feature less common for canonical translation factors. Here we generated a hemizygous Leishmania mutant of the least studied cap-binding paralog, LeishIF4E2, by eliminating one of the two alleles using the CRISPR-Cas9 methodology. The mutant showed morphological defects with short and rounded cells, and a significant reduction in their flagellar length. Moreover, the LeishIF4E2(+/-) cells were impaired in their ability to infect cultured macrophages. The mutants showed differences in their proteome: upregulated proteins were related mainly to general metabolic processes including enzymes involved in fatty acid metabolism, DNA repair and replication, signaling, and cellular motor activity. Downregulated proteins included flagellar rod and cytoskeletal proteins, as well as surface antigens involved in virulence. Overall, LeishIF4E2 does not behave like a general translation factor and its function remains elusive. It could affect translation of a particular set of transcripts, causing direct or downstream effects that do not affect global translation. Our results suggest that individual LeishIF4Es perform specific functions.

Insights into Leishmania Molecules and Their Potential Contribution to the Virulence of the Parasite

Neglected parasitic diseases affect millions of people worldwide, resulting in high morbidity and mortality. Among other parasitic diseases, leishmaniasis remains an important public health problem caused by the protozoa of the genus Leishmania, transmitted by the bite of the female sand fly. The disease has also been linked to tropical and subtropical regions, in addition to being an endemic disease in many areas around the world, including the Mediterranean basin and South America. Although recent years have witnessed marked advances in Leishmania-related research in various directions, many issues have yet to be elucidated. The intention of the present review is to give an overview of the major virulence factors contributing to the pathogenicity of the parasite. We aimed to provide a concise picture of the factors influencing the reaction of the parasite in its host that might help to develop novel chemotherapeutic and vaccine strategies.

Toxoplasma and Eimeria co-opt the host cFos expression for intracellular development in mammalian cells

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Gene expression profiles differ significantly between Toxoplasma and Eimeria-infected host cells.

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Several distinct and shared host-signaling cascades are regulated by coccidian parasites.

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cFos is one of the few host transcripts mutually regulated during infection by both pathogens.

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Host cFos is required for optimal in vitro development of E. falciformis and T. gondii.

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Transcriptomics of parasitized wild-type and cFos^-/- host cells reveals a perturbation of cFos network.

Successful asexual reproduction of intracellular pathogens depends on their potential to exploit host resources and subvert antimicrobial defense. In this work, we deployed two prevalent apicomplexan parasites of mammalian cells, namely Toxoplasma gondii and Eimeria falciformis, to identify potential host determinants of infection. Expression analyses of the young adult mouse colonic (YAMC) epithelial cells upon infection by either parasite showed regulation of several distinct transcripts, indicating that these two pathogens program their intracellular niches in a tailored manner. Conversely, parasitized mouse embryonic fibroblasts (MEFs) displayed a divergent transcriptome compared to corresponding YAMC epithelial cells, suggesting that individual host cells mount a fairly discrete response when encountering a particular pathogen. Among several host transcripts similarly altered by T. gondii and E. falciformis, we identified cFos, a master transcription factor, that was consistently induced throughout the infection. Indeed, asexual growth of both parasites was strongly impaired in MEF host cells lacking cFos expression. Last but not the least, our differential transcriptomics of the infected MEFs (parental and cFos^-/- mutant) and YAMC epithelial cells disclosed a cFos-centered network, underlying signal cascades, as well as a repertoire of nucleotides- and ion-binding proteins, which presumably act in consort to acclimatize the mammalian cell and thereby facilitate the parasite development.

Leishmania mexicana: Novel Insights of Immune Modulation through Amastigote Exosomes

Exosomes are extracellular microvesicles of endosomal origin (multivesicular bodies, MVBs) constitutively released by eukaryotic cells by fusion of MVBs to the plasma membrane. The exosomes from Leishmania parasites contain an array of parasite molecules such as virulence factors and survival messengers, capable of modulating the host immune response and thereby favoring the infection of the host. We here show that exosomes of L. mexicana amastigotes (aExo) contain the virulence proteins gp63 and PP2C. The incubation of aExo with bone marrow-derived macrophages (BMMs) infected with L. mexicana led to their internalization and were found to colocalize with the cellular tetraspanin CD63. Furthermore, aExo inhibited nitric oxide production of infected BMMs, permitting enhanced intracellular parasite survival. Expressions of antigen-presenting (major histocompatibility complex class I, MHC-I, and CD1d) and costimulatory (CD86 and PD-L1) molecules were modulated in a dose-dependent fashion. Whereas MHC-I, CD86 and PD-L1 expressions were diminished by exosomes, CD1d was enhanced. We conclude that aExo of L. mexicana are capable of decreasing microbicidal mechanisms of infected macrophages by inhibiting nitric oxide production, thereby enabling parasite survival. They also hamper the cellular immune response by diminishing MHC-I and CD86 on an important antigen-presenting cell, which potentially interferes with CD8 T cell activation. The enhanced CD1d expression in combination with reduction of PD-L1 on BMMs point to a potential shift of the activation route towards lipid presentations, yet the effectivity of this immune activation is not evident, since in the absence of costimulatory molecules, cellular anergy and tolerance would be expected.

Ecological divergence and hybridization of Neotropical Leishmania parasites

Parasites are interesting models for studying speciation processes because they have a high potential for specialization, thanks to the intimate ecological association with their hosts and vectors. Yet little is known about the circumstances under which new parasite lineages emerge. Here we studied the genome diversity of parasites of the Leishmania braziliensis species complex that inhabit both Amazonian and Andean biotas in Peru. We identify three major parasite lineages that occupy particular ecological niches and show that these emerged during forestation changes over the past 150,000 y. We furthermore discovered that meiotic recombination between Amazonian and Andean lineages resulted in full-genome hybrids presenting mixed mitochondrial genomes, providing insights into the genetic consequences of hybridization in parasitic protozoa.

The tropical Andes are an important natural laboratory to understand speciation in many taxa. Here we examined the evolutionary history of parasites of the Leishmania braziliensis species complex based on whole-genome sequencing of 67 isolates from 47 localities in Peru. We first show the origin of Andean Leishmania as a clade of near-clonal lineages that diverged from admixed Amazonian ancestors, accompanied by a significant reduction in genome diversity and large structural variations implicated in host–parasite interactions. Within the Andean species, patterns of population structure were strongly associated with biogeographical origin. Molecular clock and ecological niche modeling suggested that the history of diversification of the Andean lineages is limited to the Late Pleistocene and intimately associated with habitat contractions driven by climate change. These results suggest that changes in forestation over the past 150,000 y have influenced speciation and diversity of these Neotropical parasites. Second, genome-scale analyses provided evidence of meiotic-like recombination between Andean and Amazonian Leishmania species, resulting in full-genome hybrids. The mitochondrial genome of these hybrids consisted of homogeneous uniparental maxicircles, but minicircles originated from both parental species. We further show that mitochondrial minicircles—but not maxicircles—show a similar evolutionary pattern to the nuclear genome, suggesting that compatibility between nuclear-encoded mitochondrial genes and minicircle-encoded guide RNA genes is essential to maintain efficient respiration. By comparing full nuclear and mitochondrial genome ancestries, our data expand our appreciation on the genetic consequences of diversification and hybridization in parasitic protozoa.

Leishmania Viannia guyanensis, LRV1 virus and extracellular vesicles: a dangerous trio influencing the faith of immune response during muco-cutaneous leishmaniasis

Parasites of Leishmania genus have developed various strategies to overcome host immune response favoring its infection and development toward leishmaniasis. With an array of virulence factors, those parasites modify host macrophage signaling and functions. Depending of the species involved, visceral or cutaneous leishmaniasis will develop. Several years ago, Leishmania Viannia guyanensis that is naturally infected with the endosymbiotic virus Leishmania RNA Virus 1 was found to cause a particularly aggressive form of South-American mucocutaneous leishmaniasis. This virus, when co-transmitted with the parasite was shown to strongly modulate RNA sensors and NLRP3 inflammasome network that could explain in part the exacerbated skin pathology caused by this particular parasite. In this review, we will be discussing how this endosymbiotic virus-infected Leishmania in conjunction with Leishmania exosomes partner together to manipulate host immune response in their favor.

Probing the molecular mechanism of aggressive infection by antimony resistant Leishmania donovani

The disease visceral leishmaniasis (VL) or kala azar is caused by the protozoan parasite, Leishmania donovani (LD). For many decades the pentavalent antimonial drugs countered the successive epidemics of the disease in the Indian sub-continent and elsewhere. With time, antimony resistant LD (LD^R) developed and the drug in turn lost its efficacy. Infection of mammals with LD^R gives rise to aggressive infection as compared to its sensitive counterpart (LD^S) coupled with higher surge of IL-10 and TGF-β. The IL-10 causes upregulation of multidrug resistant protein-1 which causes efflux of antimonials from LD^R infected cells. This is believed to be a key mechanism of antimony resistance. MicroRNAs (miRNAs) are tiny post-transcriptional regulators of gene expression in mammalian cells and in macrophage play a pivotal role in controlling the expression of cytokines involved in infection process. Therefore, a change in miRNA profiles of macrophages infected with LD^S or LD^R could explain the differential cytokine response observed. Interestingly, the outcome of LD infection is also governed by the critical balance of pro- and anti-inflammatory cytokines which is inturn regulated by miRNA-Ago2 or miRNP complex and its antagonist RNA binding protein HuR. Here Ago2 plays the fulcrum whose phosphorylation and de-phosphorylation dictates the process; which in turn is controlled by PP2A and HuR. LD^S and LD^R upregulate PP2A and downregulate HuR at different magnitude leading to various levels of anti-inflammatory to proinflammatory cytokine production and resulting pathology in the host. While ectopic HuR expression alone is sufficient to clear LD^S infection, simultaneous upregulation of HuR and inhibition of PP2A is required to inhibit LD^R mediated infection. Therefore, tampering with miRNA pathway could be a new strategy to control infection caused by LD^R parasite.

Leishmania infection triggers hepcidin-mediated proteasomal degradation of Nramp1 to increase phagolysosomal iron availability

Natural resistance-associated macrophage protein 1 (Nramp1) was originally discovered as a genetic determinant of resistance against multiple intracellular pathogens, including Leishmania. It encodes a transmembrane protein of the phago-endosomal compartments, where it functions as an iron transporter. But the mechanism by which Nramp1 controls host-pathogen dynamics and determines final outcome of an infection is yet to be fully deciphered. Whether the expression of Nramp1 is altered in response to a pathogen attack is also unknown. To address these, Nramp1 status was examined in Leishmania major-infected murine macrophages. We observed that at 12 hrs post infection, there was drastic lowering of Nramp1 level accompanied by increased phagolysosomal iron content and enhanced intracellular parasite growth. Leishmania infection-induced Nramp1 downregulation was caused by ubiquitin-proteasome degradation pathway, which in turn was found to be mediated by the iron-regulatory peptide hormone hepcidin. Blocking of Nramp1 degradation with proteasome inhibitor or transcriptional agonist of hepcidin resulted in depletion of phagolysosomal iron pool that led to significant reduction of intracellular parasite burden. Interestingly, Nramp1 level was restored to normalcy after 30 hrs of infection with a concomitant drop in phagolysosomal iron, which is suggestive of a host counteractive response to deprive the pathogen of this essential micronutrient. Taken together, our study implicates Nramp1 as a central player in the host-pathogen battle for phagolysosomal iron. We also report Nramp1 as a novel target for hepcidin, and this 'hepcidin-Nramp1' axis may have a broader role in regulating macrophage iron homeostasis.

Detection of Metalloproteases and Cysteine Proteases RNA Transcripts of Leishmania (Leishmania) infantum in Ear Edge Skin of Naturally Infected Dogs

Leishmania spp. proteases have been proposed as virulence factors contributing to adaptive success these parasites to the mammalian hosts. Since these enzymes are poorly studied in naturally infected dogs, this work aims to show the differences in metalloprotease and cysteine proteases gene expression in ear edge skin of dogs naturally infected by Leishmania (Leishmania) infantum. A cohort of dogs (n = 20) naturally infected by L. (L.) infantum was clinically classified as asymptomatic, oligosymptomatic, and polysymptomatic and the parasite load range estimated. The analysis of proteases expression by RT-PCR in the ear edge skin was also assessed, suggesting more transcripts of proteases in cDNA samples from polysymptomatic dogs than oligosymptomatic and asymptomatic ones. Metalloprotease RT-PCR assays yielded products (202 bp) in all assessed cDNA dog samples. In contrast, cysteine proteases transcripts (227 bp) had shown to be better detected in cDNA samples of polysymptomatic dogs, compared with cDNA samples from asymptomatic and oligosymptomatic dogs. Predictive in silico assays suggested that secondary structures of metalloproteasee mRNAs can be more stable than cysteine proteases at the skin temperature of dogs. Evidence is presented that during natural infection of dogs by L. (L.) infantum, this parasite produces transcripts of metalloprotease and cysteine protease RNA in the skin from asymptomatic, oligosymptomatic, and polysymptomatic dogs.

MicroRNA exporter HuR clears the internalized pathogens by promoting pro-inflammatory response in infected macrophages

HuR is a miRNA derepressor protein that can act as miRNA sponge for specific miRNAs to negate their action on target mRNAs. Here we have identified how HuR, by inducing extracellular vesicles‐mediated export of miRNAs, ensures robust derepression of miRNA‐repressed cytokines essential for strong pro‐inflammatory response in activated mammalian macrophages. Leishmania donovani, the causative agent of visceral leishmaniasis, on the contrary alters immune response of the host macrophage by a variety of complex mechanisms to promote anti‐inflammatory response essential for the survival of the parasite. We have found that during Leishmania infection, the pathogen targets HuR to promote onset of anti‐inflammatory response in mammalian macrophages. In infected macrophages, Leishmania also upregulate protein phosphatase 2A that acts on Ago2 protein to keep it in dephosphorylated and miRNA‐associated form. This causes robust repression of the miRNA‐targeted pro‐inflammatory cytokines to establish an anti‐inflammatory response in infected macrophages. HuR has an inhibitory effect on protein phosphatase 2A expression, and mathematical modelling of macrophage activation process supports antagonistic miRNA‐modulatory roles of HuR and protein phosphatase 2A which mutually balances immune response in macrophage by targeting miRNA function. Supporting this model, ectopic expression of the protein HuR and simultaneous inhibition of protein phosphatase 2A induce strong pro‐inflammatory response in the host macrophage to prevent the virulent antimonial drug‐sensitive or drug‐resistant form of L. donovani infection. Thus, HuR can act as a balancing factor of immune responses to curtail the macrophage infection process by the protozoan parasite.

SILAC-based quantitative proteomics reveals pleiotropic, phenotypic modulation in primary murine macrophages infected with the protozoan pathogen Leishmania donovani

Leishmaniases are major vector-borne tropical diseases responsible for great human morbidity and mortality, caused by protozoan, trypanosomatid parasites of the genus Leishmania. In the mammalian host, parasites survive and multiply within mononuclear phagocytes, especially macrophages. However, the underlying mechanisms by which Leishmania spp. affect their host are not fully understood. Herein, proteomic alterations of primary, bone marrow-derived BALB/c macrophages are documented after 72 h of infection with Leishmania donovani insect-stage promastigotes, applying a SILAC-based, quantitative proteomics approach. The protocol was optimised by combining strong anion exchange and gel electrophoresis fractionation that displayed similar depth of analysis (combined total of 6189 mouse proteins). Our analyses revealed 86 differentially modulated proteins (35 showing increased and 51 decreased abundance) in response to Leishmania donovani infection. The proteomics results were validated by analysing the abundance of selected proteins. Intracellular Leishmania donovani infection led to changes in various host cell biological processes, including primary metabolism and catabolic process, with a significant enrichment in lysosomal organisation. Overall, our analysis establishes the first proteome of bona fide primary macrophages infected ex vivo with Leishmania donovani, revealing new mechanisms acting at the host/pathogen interface. SIGNIFICANCE: Little is known on proteome changes that occur in primary macrophages after Leishmania donovani infection. This study describes a SILAC-based quantitative proteomics approach to characterise changes of bone marrow-derived macrophages infected with L. donovani promastigotes for 72 h. With the application of SILAC and the use of SAX and GEL fractionation methods, we have tested new routes for proteome quantification of primary macrophages. The protocols developed here can be applicable to other diseases and pathologies. Moreover, this study sheds important new light on the "proteomic reprogramming" of infected macrophages in response to L. donovani promastigotes that affects primary metabolism, cellular catabolic processes, and lysosomal/vacuole organisation. Thus, our study reveals key molecules and processes that act at the host/pathogen interface that may inform on new immuno- or chemotherapeutic interventions to combat leishmaniasis.

LeishIF4E1 Deletion Affects the Promastigote Proteome, Morphology, and Infectivity

Leishmania parasites are the causative agents of a broad spectrum of diseases. The parasites migrate between sand-fly vectors and mammalian hosts, adapting to changing environments by driving a regulated program of gene expression, with translation regulation playing a key role. The leishmanias encode six different paralogs of eIF4E, the cap-binding translation initiation factor. Since these vary in function, expression profile, and assemblage, it is assumed that each is assigned a specific role throughout the life cycle. Using the CRISPR-Cas9 system for Leishmania, we generated a null mutant of LeishIF4E1, eliminating both alleles. Although the mutant cells were viable, their morphology was altered and their ability to synthesize the flagellum was impaired. Elimination of LeishIF4E1 affected their protein expression profile and decreased their ability to infect cultured macrophages. Restoring LeishIF4E1 expression restored the affected features. This study highlights the importance of LeishIF4E1 in diverse cellular events during the life cycle of Leishmania.

Leishmania parasites cycle between sand-fly vectors and mammalian hosts, adapting to changing environmental conditions by driving a stage-specific program of gene expression, which is tightly regulated by translation processes. Leishmania encodes six eIF4E orthologs (LeishIF4Es) and five eIF4G candidates, forming different cap-binding complexes with potentially varying functions. Most LeishIF4E paralogs display temperature sensitivity in their cap-binding activity, except for LeishIF4E1, which maintains its cap-binding activity under all conditions. We used the CRISPR-Cas9 system to successfully generate a null mutant of LeishIF4E1 and examine how its elimination affected parasite physiology. Although the LeishIF4E1^–/– null mutant was viable, its growth was impaired, in line with a reduction in global translation. As a result of the mutation, the null LeishIF4E1^–/– mutant had a defective morphology, as the cells were round and unable to grow a normal flagellum. This was further emphasized when the LeishIF4E1^–/– cells failed to develop the promastigote morphology once they shifted from conditions that generate axenic amastigotes (33°C, pH 5.5) back to neutral pH and 25°C, and they maintained their short flagellum and circular structure. Finally, the LeishIF4E1^–/– null mutant displayed difficulty in infecting cultured macrophages. The morphological changes and reduced infectivity of the mutant may be related to differences in the proteomic profile of LeishIF4E1^–/– cells from that of controls. All defects monitored in the LeishIF4E1^–/– null mutant were reversed in the add-back strain, in which expression of LeishIF4E1 was reconstituted, establishing a strong link between the cellular defects and the absence of LeishIF4E1 expression.

IMPORTANCELeishmania parasites are the causative agents of a broad spectrum of diseases. The parasites migrate between sand-fly vectors and mammalian hosts, adapting to changing environments by driving a regulated program of gene expression, with translation regulation playing a key role. The leishmanias encode six different paralogs of eIF4E, the cap-binding translation initiation factor. Since these vary in function, expression profile, and assemblage, it is assumed that each is assigned a specific role throughout the life cycle. Using the CRISPR-Cas9 system for Leishmania, we generated a null mutant of LeishIF4E1, eliminating both alleles. Although the mutant cells were viable, their morphology was altered and their ability to synthesize the flagellum was impaired. Elimination of LeishIF4E1 affected their protein expression profile and decreased their ability to infect cultured macrophages. Restoring LeishIF4E1 expression restored the affected features. This study highlights the importance of LeishIF4E1 in diverse cellular events during the life cycle of Leishmania.

The host cell secretory pathway mediates the export of Leishmania virulence factors out of the parasitophorous vacuole

To colonize phagocytes, Leishmania subverts microbicidal processes through components of its surface coat that include lipophosphoglycan and the GP63 metalloprotease. How these virulence glycoconjugates are shed, exit the parasitophorous vacuole (PV), and traffic within host cells is poorly understood. Here, we show that lipophosphoglycan and GP63 are released from the parasite surface following phagocytosis and redistribute to the endoplasmic reticulum (ER) of macrophages. Pharmacological disruption of the trafficking between the ER and the Golgi hindered the exit of these molecules from the PV and dampened the cleavage of host proteins by GP63. Silencing by RNA interference of the soluble N-ethylmaleimide-sensitive-factor attachment protein receptors Sec22b and syntaxin-5, which regulate ER-Golgi trafficking, identified these host proteins as components of the machinery that mediates the spreading of Leishmania effectors within host cells. Our findings unveil a mechanism whereby a vacuolar pathogen takes advantage of the host cell's secretory pathway to promote egress of virulence factors beyond the PV.

Leishmania promastigotes are internalized by phagocytes into a highly modified phagosome that promotes parasite growth and differentiation into the amastigote form. To survive in the phagosome, Leishmania employs surface-bound glycoconjugates such as the GP63 metalloprotease and lipophosphoglycan to subvert the phagosome’s microbicidal potential. In particular, GP63 cleaves host cell vesicle fusion molecules that regulate phagosomal processes ranging from antigen cross-presentation to cytokine secretion. Unlike apicomplexan parasites and bacteria, Leishmania does not inject its virulence-associated glycoconjugates across the phagosome membrane. We found that post-phagocytosis, Leishmania co-opts the host cell secretory pathway to promote the egress of its virulence factors out of the phagosome. Importantly, chemical and genetic inhibition of endoplasmic reticulum (ER) to Golgi transport hindered the redistribution of GP63 and lipophosphoglycan, thereby impeding the cleavage of GP63 target Synaptotagmin XI. Notably, knockdown ER/ERGIC-resident membrane fusion regulators Sec22b and syntaxin-5 revealed that these host molecules were essential to the phagosomal egress of Leishmania virulence factors. These findings provide new insight into how Leishmania sabotages the host cell endomembrane system for its own benefit.

A Therapeutic Approach Against Leishmania donovani by Predicting RNAi Molecules Against the Surface Protein, gp63

Background:

Leishmaniasis is a disease caused by the Leishmania sp. and can be classified into two major types: cutaneous and visceral leismaniasis. Visceral leishmaniasis is the deadlier type and is mediated by Leishmania donovani and involves the establishment of persistent infection and causes damage to the liver, spleen and bone marrow. With no vaccine yet available against leishmaniasis and the current therapeutic drugs of leishmaniasis being toxic and expensive; an alternative treatment is necessary.

Objective:

Surface glycocalyx protein gp63, plays a major role in the virulence and resulting pathogenicity associated with the disease. Henceforth, silencing the gp63 mRNA through the RNA interference system was the aim of this study.

Methods:

In this study two competent siRNAs and three miRNAs have been designed against gp63 for five different strains of L. donovani by using various computational methods. Target specific siRNAs were designed using siDirect 2.0 and to design possible miRNA, another tool named IDT (IntegratedDNA Technology). Screening for off-target similarity was done by BLAST and the GC contents and the secondary structures of the designed RNAs were determined. RNA-RNA interaction was calculated by RNAcofold and IntraRNA, followed by the determination of heat capacity and the concentration of duplex by DNAmelt web server.

Results:

The selected RNAi molecules; two siRNA and three miRNA had no off-target in human genome and the ones with lower GC content were selected for efficient RNAi function. The selected ones showed proper thermodynamic characteristics to suppress the expression of the pathogenic gene of gp63.

Macrophage priming is dispensable for NLRP3 inflammasome activation and restriction of Leishmania amazonensis replication

The NLRP3 inflammasome is activated in response to multiple stimuli and triggers activation of caspase-1 (CASP1), IL-1β production, and inflammation. NLRP3 activation requires two signals. The first leads to transcriptional regulation of specific genes related to inflammation, and the second is triggered when pathogens, toxins, or specific compounds damage cellular membranes and/or trigger the production of reactive oxygen species (ROS). Here, we assess the requirement of the first signal (priming) for the activation of the NLRP3 inflammasome in bone marrow-derived macrophages (BMDMs) infected with Leishmania amazonensis. We found that BMDMs express the inflammasome components NLRP3, ASC, and CASP1 at sufficient levels to enable the assembly and activation of NLRP3 inflammasome in response to infection. Therefore, priming was not required for the formation of ASC specks, CASP1 activation (measured by fluorescent dye FAM-YVAD), and restriction of L. amazonensis replication via the NLRP3 inflammasome. By contrast, BMDM priming was required for CASP1 cleavage (p20) and IL-1β secretion, because priming triggers robust up-regulation of pro-IL-1β and CASP11 that are important for efficient processing of CASP1 and IL-1β. Taken together, our data shed light into the cellular and molecular processes involved in activation of the NLRP3 in macrophages by Leishmania, a process that is important for the outcome of Leishmaniasis.

Modulation of Host-Pathogen Communication by Extracellular Vesicles (EVs) of the Protozoan Parasite Leishmania

Leishmania genus protozoan parasites have developed various strategies to overcome host cell protective mechanisms favoring their survival and propagation. Recent findings in the field propose a new player in this infectious strategy, the Leishmania exosomes. Exosomes are eukaryotic extracellular vesicles essential to cell communication in various biological contexts. In fact, there have been an increasing number of reports over the last 10 years regarding the role of protozoan parasite exosomes, Leishmania exosomes included, in their capacity to favor infection and propagation within their hosts. In this review, we will discuss the latest findings regarding Leishmania exosome function during infectious conditions with a strong focus on Leishmania-host interaction from a mammalian perspective. We also compare the immunomodulatory properties of Leishmania exosomes to other parasite exosomes, demonstrating the conserved, important role that exosomes play during parasite infection.

In silico characterization of multiple genes encoding the GP63 virulence protein from Leishmania braziliensis: identification of sources of variation and putative roles in immune evasion

Background

The leishmaniasis are parasitic diseases caused by protozoans of the genus Leishmania, highly divergent eukaryotes, characterized by unique biological features. To survive in both the mammalian hosts and insect vectors, these pathogens make use of a number of mechanisms, many of which are associated with parasite specific proteases. The metalloprotease GP63, the major Leishmania surface antigen, has been found to have multiple functions required for the parasite’s survival. GP63 is encoded by multiple genes and their copy numbers vary considerably between different species and are increased in those from the subgenus Viannia, including L. braziliensis.

Results

By comparing multiple sequences from Leishmania and related organisms this study sought to characterize paralogs in silico, evaluating their differences and similarities and the implications for the GP63 function. The Leishmania GP63 genes are encoded on chromosomes 10, 28 and 31, with the genes from the latter two chromosomes more related to genes found in insect or plant parasites. Those from chromosome 10 have experienced independent expansions in numbers in Leishmania, especially in L. braziliensis. These could be clustered in three groups associated with different mRNA 3′ untranslated regions as well as distinct C-terminal ends for the encoded proteins, with presumably distinct expression patterns and subcellular localizations. Sequence variations between the chromosome 10 genes were linked to intragenic recombination events, mapped to the external surface of the proteins and predicted to be immunogenic, implying a role against the host immune response.

Conclusions

Our results suggest a greater role for the sequence variation found among the chromosome 10 GP63 genes, possibly related to the pathogenesis of L. braziliensis and closely related species within the mammalian host. They also indicate different functions associated to genes mapped to different chromosomes. For the chromosome 10 genes, variable subcellular localizations were found to be most likely associated with multiple functions and target substrates for this versatile protease.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5465-z) contains supplementary material, which is available to authorized users.

The effects of CCR7 and related signaling pathways on Leishmania major -infected human dendritic cells

OBJECTIVES

In our research, we aimed to investigate the roles of CC-chemokine receptor 7 (CCR7) and relevant signaling pathways in Leishmania major-infected human dendritic cells (DCs).

METHODS

Differentially expressed genes (DEGs) in L. major-infected human DCs were selected out and visualized using R program. Kyoto Encyclopedia of Genes and Genomes pathway analysis was conducted for investigation of significantly enriched signaling pathways and Gene Ontology enrichment analysis was carried out for the unveiling of enriched Molecular Functions and Biological Processes in L. major-infected human DCs. Besides, Hub gene was screened out using weighted gene coexpression network analysis and Cytoscape. In addition, enzyme-linked immunosorbent assay and real-time quantitative polymerase chain reaction were used for detection of relative expression of CCR7, interleukin-12 (IL-12), and interferon-γ (IFN-γ) in L. major-infected human DCs and western blot analysis was used for detection of relative expression of CCR7 and other proteins in JAK-STAT signaling pathway in L. major-infected human DCs.

RESULTS

CCR7 was upregulated and both chemokine and JAK-STAT signaling pathway were activated in L. major-infected human DCs. During the L. major infection, total number of L. major-infected human DCs were increased, as well as the relative expression levels of CCR7, IL-12, and IFN-γ and proteins in the JAK-STAT signaling pathway. Overexpression of CCR7 not only increased expression levels of IL-12 and IFN-γ but also activated the JAK-STAT signaling pathway to affect the leishmaniasis progression.

CONCLUSION

L. major infection-induced activation of CCR7, as well as JAK2 and STAT1, might well upregulate the expression of BAX yet suppress the expression of both Bcl2 and c-Jun to affect leishmaniasis progression.

More than just exosomes: distinct Leishmania infantum extracellular products potentiate the establishment of infection

The use of secretion pathways for effector molecule delivery by microorganisms is a trademark of pathogenesis. Leishmania extracellular vesicles (EVs) were shown to have significant immunomodulatory potential. Still, they will act in conjunction with other released parasite-derived products that might modify the EVs effects. Notwithstanding, the immunomodulatory properties of these non-vesicular components and their influence in the infectious process remains unknown. To address this, we explored both in vitro and in vivo the immunomodulatory potential of promastigotes extracellular material (EXO), obtained as a whole or separated in two different fractions: EVs or vesicle depleted EXO (VDE). Using an air pouch model, we observed that EVs and VDE induced a dose-dependent cell recruitment profile different from the one obtained with parasites, attracting significantly fewer neutrophils and more dendritic cells (DCs). Additionally, when we co-inoculated parasites with extracellular products a drop in cell recruitment was observed. Moreover, in vitro, while VDE (but not EVs) downregulated the expression of DCs and macrophages activation markers, both products were able to diminish the responsiveness of these cells to LPS. Finally, the presence of Leishmania infantum extracellular products in the inoculum promoted a dose-dependent infection potentiation in vivo, highlighting their relevance for the infectious process. In conclusion, our data demonstrate that EVs are not the only relevant players among the parasite exogenous products. This, together with the dose-dependency observed, opens new avenues to the comprehension of Leishmania infectious process. The approach presented here should be exploited to revisit existing data and considered for future studies in other infection models.

Extracellular release of virulence factor major surface protease via exosomes in Leishmania infantum promastigotes

Background

The Leishmania spp. protozoa are introduced into humans through a sand fly blood meal, depositing the infectious metacyclic promastigote form of the parasite into human skin. Parasites enter a variety of host cells, although a majority are found in macrophages where they replicate intracellularly during chronic leishmaniasis. Symptomatic leishmaniasis causes considerable human morbidity in endemic regions. The Leishmania spp. evade host microbicidal mechanisms partially through virulence-associated proteins such as the major surface protease (MSP or GP63), to inactivate immune factors in the host environment. MSP is a metalloprotease encoded by a tandem array of genes belonging to three msp gene classes, whose mRNAs are differentially expressed in different life stages of the parasite. Like other cells, Leishmania spp. release small membrane-bound vesicles called exosomes into their environment. The purpose of this study was to detect MSP proteins in exosomal vesicles of Leishmania spp. protozoa.

Methods

Using mass spectrometry data we determined the profile of MSP class proteins released in L. infantum exosomes derived from promastigotes in their avirulent procyclic (logarithmic) stage and virulent stationary and metacyclic stages. MSP protein isoforms belonging to each of the three msp gene classes could be identified by unique peptides.

Results

Metacyclic promastigote exosomes contained the highest, and logarithmic exosomes had the lowest abundance of total MSP. Among the MSP classes, MSPC class had the greatest variety of isoforms, but was least abundant in all exosomes. Nonetheless, all MSP classes were present at higher levels in exosomes released from stationary or metacyclic promastigotes than logarithmic promastigotes.

Conclusions

The data suggest the efficiency of exosome release may be more important than the identity of MSP isoform in determining the MSP content of Leishmania spp. exosomes.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2937-y) contains supplementary material, which is available to authorized users.