Increasing in cysteine proteinase B expression and enzymatic activity during in vitro differentiation of Leishmania (Viannia) braziliensis: First evidence of modulation during morphological transition

Effect of the aggregated protein dye YAT2150 on Leishmania parasite viability

The problems associated with the drugs currently used to treat leishmaniasis, including resistance, toxicity, and the high cost of some formulations, call for the urgent identification of new therapeutic agents with novel modes of action. The aggregated protein dye YAT2150 has been found to be a potent antileishmanial compound, with a half-maximal inhibitory concentration (IC50) of approximately 0.5 µM against promastigote and amastigote stages of Leishmania infantum. The encapsulation in liposomes of YAT2150 significantly improved its in vitro IC50 to 0.37 and 0.19 µM in promastigotes and amastigotes, respectively, and increased the half-maximal cytotoxic concentration in human umbilical vein endothelial cells to >50 µM. YAT2150 became strongly fluorescent when binding intracellular protein deposits in Leishmania cells. This fluorescence pattern aligns with the proposed mode of action of this drug in the malaria parasite Plasmodium falciparum, the inhibition of protein aggregation. In Leishmania major, YAT2150 rapidly reduced ATP levels, suggesting an alternative antileishmanial mechanism. To the best of our knowledge, this first-in-class compound is the only one described so far having significant activity against both Plasmodium and Leishmania, thus being a potential drug for the treatment of co-infections of both parasites.

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.

Promastigote-to-Amastigote Conversion in Leishmania spp.—A Molecular View

A key factor in the successful infection of a mammalian host by Leishmania parasites is their conversion from extracellular motile promastigotes into intracellular amastigotes. We discuss the physical and chemical triggers that induce this conversion and the accompanying changes at the molecular level crucial for the survival of these intracellular parasites. Special emphasis is given to the reliance of these trypanosomatids on the post-transcriptional regulation of gene expression but also to the role played by protein kinases, chaperone proteins and proteolytic enzymes. Lastly, we offer a model to integrate the transduction of different stress signals for the induction of stage conversion.

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.

Novel Insights Into Leishmania (Viannia) braziliensis In Vitro Fitness Guided by Temperature Changes Along With Its Subtilisins and Oligopeptidase B

Proteases are virulence factors with a recognized impact on the Leishmania spp. life cycle. This study considers a set of analyses measuring phenotypic factors of L. (V.) braziliensis clinical isolates as promastigotes growth curves, murine peritoneal macrophages infection, inflammatory mediators production, and serine proteases gene expression (subtilisin 13: S13, subtilisin 28: S28, oligopeptidase B: OPB) assessing these isolates’ fitness on in vitro conditions. Parasites had different behavior during the early growth phase from day zero to day three, and all isolates reached the stationary growth phase between days four and seven. Macrophages infection showed two tendencies, one of decreased infection rate and number of parasites per macrophage (Infection Index <1000) and another with a constant infection index (≥1400). TNF-α (≥10 pg/mL) detected in infections by 75% of isolates, IL-6 (≥80 pg/mL) by 30% of isolates and low levels of NO (≥0.01µM) in almost all infections. Gene expression showed higher values of S13 (≥2RQ) in the intracellular amastigotes of all the isolates evaluated. On the contrary, S28 expression was low (≤1RQ) in all isolates. OPB expression was different between promastigotes and intracellular amastigotes, being significantly higher (≥2RQ) in the latter form of 58% of the isolates. Predictive structural assays of S13 and OPB were performed to explore temperature influence on gene expression and the encoded proteases. Gene expression data is discussed based on in silico predictions of regulatory regions that show plasticity in the linearity index of secondary structures of S13 and OPB 3’-untranslated regions of mRNA, dependent on temperature changes. While hairpin structures suggest an active region of mRNA for both genes above 26°C, pseudoknot structure found in S13 is an indication of a particular profile of this gene at mammalian host temperatures (37°C). Furthermore, the predicted 3D structures are in accordance with the influence of these temperatures on the catalytic site stability of both enzymes, favoring their action over peptide substrates. Data gathered here suggest that L. (V.) braziliensis serine proteases can be influenced by the temperature conditions affecting parasite fitness throughout its life cycle.

Axenic amastigotes of Leishmania species as a suitable model for in vitro studies

Leishmania spp. are etiological agents of infection diseases, which in some cases can be fatal. The main forms of their biological cycle, promastigotes and amastigotes, can be maintained in vitro. While promastigotes are easier to maintain, amastigotes are more complex and can be obtained through different ways, including infection assays of tissues or in vitro cells, and differentiation from promastigotes to axenic amastigotes. Several protocols have been proposed for in vitro differentiation for at least 12 Leishmania spp. of both subgenera, Leishmania and Viannia. In this review we propose a critical summary of axenic amastigotes induction, as well as the impact of these strategies on metabolic pathways and regulatory networks analyzed by omics approaches. The parameters used by different research groups show considerable variations in temperature, pH and induction stages, as highlighted here for Leishmania (Viannia) braziliensis. Therefore, a consensus on strategies for inducing amastigogenesis is necessary to improve accuracy and even define stage-specific biomarkers. In fact, the axenic amastigote model has contributed to elucidate several aspects of the parasite cycle, however, since it does not reproduce the intracellular environment, its use requires several precautions. In addition, we present a discussion about using axenic amastigotes for drug screening, suggesting the need of a more sensitive methodology to verify cell viability in these tests. Collectively, this review explores the advantages and limitations found in studies with axenic amastigotes, done for more than 30 years, and discuss the gaps that impair their use as a suitable model for in vitro studies.

Serine proteases profiles of Leishmania (Viannia) braziliensis clinical isolates with distinct susceptibilities to antimony

Glucantime (Sb^V) is the first-line treatment against American Tegumentary Leishmaniasis. Resistance cases to this drug have been reported and related to host characteristics and parasite phenotypes. In this study, 12 Leishmania (Viannia) braziliensis isolates from patients that presented clinical cure (Responders—R) and relapse or therapeutic failure (Non-responders—NR) after treatment with antimony, were analyzed. These parasites were assessed by in vitro susceptibility to Sb^III and Sb^V, serine proteases activity measured with substrate (z-FR-AMC) and specific inhibitors (TLCK, AEBSF and PMSF). In vitro susceptibility of axenic amastigotes to Sb^III showed a significant difference between R and NR groups. The protease assays showed that TLCK inhibited almost 100% of activity in both axenic amastigotes and promastigotes while AEBSF inhibited around 70%, and PMSF showed lower inhibition of some isolates. Principal component and clustering analysis performed with these data yielded one homogeneous cluster with only NR isolates and three heterogeneous clusters with R and NR isolates. Additionally, differential expression of subtilisins (LbrM.13.0860 and LbrM.28.2570) and TXNPx (LbrM.15.1080) was evaluated in promastigotes and axenic amastigotes from both groups. The results showed a higher expression of LbrM.13.0860 and LbrM.15.1080 genes in axenic amastigotes, while LbrM.28.2570 gene had the lowest expression in all isolates, regardless of the parasite form. The data presented here show a phenotypic heterogeneity among the parasites, suggesting that exploration of in vitro phenotypes based on Sb^III and serine proteases profiles can aid in the characterization of L. (V.) braziliensis clinical isolates.

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.

A proteomics analysis of the ovarian development in females of Haemaphysalis longicornis

Haemaphysalis longicornis is an ixodid tick that can spread a wide variety of pathogens, affecting humans, livestock and wildlife health. The high reproductive capability of this species is initiated by the ingestion of a large amount of blood ingested by the engorged female tick. The degree of ovarian development is proportional to the number of eggs laid. Studying the regulatory mechanism of tick ovary development is relevant for the development of novel tick control methods. In this study, we used quantitative proteomics to study the dynamic changes in protein expression and protein phosphorylation during ovarian development of engorged female H. longicornis ticks. Synergistic action of many proteins (n = 3031) is required to achieve ovarian development and oocyte formation rapidly. Through bioinformatics analysis, changes in protein expressions and phosphorylation modifications in regulating the ovarian development of female ticks are described. Many proteins play an essential role during ovarian development. Also, protein phosphorylation appeared an important reproductive strategy to enable ticks to efficiently convert large amounts of blood in the ovaries into egg-producing components and ultimately produce many eggs.

Mapping Alterations Induced by Long-Term Axenic Cultivation of Leishmania amazonensis Promastigotes With a Multiplatform Metabolomic Fingerprint Approach

Leishmaniases are widespread neglected diseases with an incidence of 1.6 million new cases and 40 thousand deaths per year. Leishmania parasites may show distinct, species-specific patterns of virulence that lead to different clinical manifestations. It is well known that successive in vitro passages (SIVP) lead to the attenuation of virulence, but neither the metabolism nor the pathways involved in these processes are well understood. Herein, promastigotes of a virulent L. amazonensis strain recently isolated from mice was compared to SIVP derived and attenuated promastigotes, submitted to 10, 40, and 60 axenic passages and named R10, R40, and R60, respectively. In vitro assays and in vivo tests were performed to characterize and confirmed the attenuation profiles. A metabolomic fingerprint comparison of R0, R10, and R60 was performed by means of capillary electrophoresis, liquid and gas chromatography coupled to mass spectrometry. To validate the metabolomic data, qPCR for selected loci, flow cytometry to measure aPS exposure, sensitivity to antimony tartrate and ROS production assays were conducted. The 65 identified metabolites were clustered in biochemical categories and mapped in eight metabolic pathways: ABC transporters; fatty acid biosynthesis; glycine, serine and threonine metabolism; β-alanine metabolism; glutathione metabolism; oxidative phosphorylation; glycerophospholipid metabolism and lysine degradation. The obtained metabolomic data correlated with previous proteomic findings of the SVIP parasites and the gene expression of 13 selected targets. Late SIVP cultures were more sensitive to Sb^III produced more ROS and exposed less phosphatidylserine in their surface. The correspondent pathways were connected to build a biochemical map of the most significant alterations involved with the process of attenuation of L. amazonensis. Overall, the reported data pointed out to a very dynamic and continuous metabolic reprogramming process, accompanied by changes in energetic, lipid and redox metabolisms, membrane remodeling and reshaping of parasite-host cells interactions, causing impacts in chemotaxis, host inflammatory responses and infectivity at the early stages of infection.

Exploring Leishmania infantum cathepsin as a new molecular marker for phylogenetic relationships and visceral leishmaniasis diagnosis

Background

Leishmania infantum, the etiological agent of visceral leishmaniasis, is a neglected zoonosis that requires validation and standardization of satisfactory diagnostic methodologies. Thus, the aim of the present study was to evaluate the effectiveness of cathepsin L-like protease as a target for making molecular diagnoses and as a phylogenetic marker enabling to understand the intraspecies variations and evolutionary history of L. infantum in Brazil.

Methods

We used 44 isolates of L. infantum. The cathepsin L-like gene fragments were amplified, sequenced, manually aligned and analyzed using inference methods. The sequences generated were used to search and design oligonucleotide primers to be used in reactions specific to the target parasite.

Results

The cathepsin L-like gene did not show any intraspecies variability among the isolates analyzed. The pair of primers proposed amplified the target deoxyribonucleic acid (DNA) of L. infantum isolates and were effective for DNA amplification at concentrations of as low as 10^− 11 ng/μl. The proposed marker did not present cross-reactions with other hemoparasites. When used for making the diagnosis in a panel of clinical samples from dogs, a positivity rate of 49.03% (102/208) was obtained, versus 14.42% (30/208) for a ribosomal internal transcribed spacer (ITS) marker. In samples from sandflies, the rate was 6.25% and from humans, 14.28%.

Conclusions

The results described in this work allow us to infer that CatLeish-PCR is a sensitive and specific marker for use in diagnostic trials of L. infantum and in clinical and epidemiological surveys.

B-1 lymphocytes are able to produce IL-10, but is not pathogenic during Leishmania (Leishmania) amazonensis infection

Over the years research has found an association between B lymphocytes and pathogenesis during Leishmania sp. infections. Recently we demonstrated that B-2 lymphocytes are the main producers of IL-10 during L. amazonensis infection, and that the disease severity in BALB/c mice was attributed to these IL-10-producing B-2 lymphocytes. Here, we aim to understand the role of peritoneal B-1 lymphocytes in the pathogenesis of L. amazonensis infection. We found that infection resulted in a decrease in the number of B-1a lymphocytes and increase in B-1b lymphocytes in the peritoneal cavity of WT BALB/c mice but not in B lymphocyte deficient mice (BALB/Xid) mice. In vitro interaction between B-1 lymphocytes and L. amazonensis showed that the amastigote form of the parasite was able to induce higher levels of IL-10 in B-1 lymphocytes derived from infected BALB/c mice than the promastigote. Moreover, B-1 lymphocytes derived from infected mice produced more IL-10 than B-1 lymphocytes derived from naïve mice under amastigote interaction. However, the repopulation of BALB/Xid mice with B-1 lymphocytes from WT BALB/c mice did not affect the lesion development. Together, these results suggest that although B-1 lymphocytes are able to produce IL-10 during in vitro interaction with L. amazonensis, they are not directly related to pathogenesis in vivo.

Leishmania mexicana differentiation involves a selective plasma membrane autophagic-like process

Parasites of the Leishmania genus, which are the causative agents of leishmaniasis, display a complex life cycle, from a flagellated form (promastigotes) residing in the midgut of the phlebotomine vector to a non-flagellated form (amastigote) invading the mammalian host. The cellular process for the conversion between these forms is an interesting biological phenomenon involving modulation of the plasma membrane. In this study, we describe a selective autophagic-like process during the in vitro differentiation of Leishmania mexicana promastigote to amastigote-like cells. This process is responsible for size reduction and shape change of the promastigote (15-20 μm long) to the rounded amastigote-like form (4-5 μm long), identical to the one that infects host macrophages. This autophagic-like process is characterized by a profound folding of the plasma membrane and the presence of abundant cytoplasmic lipid droplets that may be the product of changes in the lipid metabolism. The key feature for the differentiation process at either pH 7.0 or pH 5.5 is the shift in temperature from 25 to 35 °C. Flagella shortening during the differentiation process appears as the product of continuous flagellar microtubular disassembly that is also accompanied by changes in mitochondrion localization. Drugs directed at blocking the parasite autophagic-like process could be important as new strategies to fight the disease.

Evidence of Subpopulations with Distinct Biological Features Within a Leishmania (Viannia) braziliensis Strain

The present study demonstrates that the Leishmania (Viannia) braziliensis strain MCAN/BR/1998/R619 is composed of multiple subpopulations with measurable distinctions. Single parasites were separated from a culture of promastigotes in stationary phase by cell sorting and then cultivated as subpopulations. Subsequently, these subpopulations were evaluated for features of in vitro growth, infectivity to murine macrophages and proteinase gene expression. The first evidence of distinct characteristics was observed during the in vitro cultivation of isolated subpopulations, as distinct clusters of patterns were formed among the cultures, indicating the existence of quantifiable fluctuations in metrics. Further, when infecting murine macrophages, the subpopulations induced distinct patterns of production of immune response mediators. While some subpopulations mainly induced the production of IL-1β, IL-6 and TNF-α, others induced the production of IL-12p70 and nitric oxide. Finally, amastigotes of these subpopulations had higher expression of proteinase genes than promastigotes. Additionally, cysteine proteinase, serine proteinase, metalloproteinase and aspartic proteinases were differentially expressed in promastigote and amastigote forms. These data suggest the existence of distinct profiles for the L. (V.) braziliensis MCAN/BR/1998/R619 strain and subpopulations that could drive the success of parasite adaptation to the environments that they inhabit.