In vitro infectivity and differential gene expression of Leishmania infantum metacyclic promastigotes: negative selection with peanut agglutinin in culture versus isolation from the stomodeal valve of Phlebotomus perniciosus

Leishmania braziliensis exosomes activate human macrophages to produce proinflammatory mediators

Exosomes, organelles measuring 30-200nm, are secreted by various cell types. Leishmania exosomes consist of many proteins, including heat shock proteins, annexins, Glycoprotein 63, proteins exerting signaling activity and those containing mRNA and miRNA. Studies have demonstrated that Leishmania donovani exosomes downregulate IFN-γ and inhibit the expression of microbicidal molecules, such as TNF and nitric oxide, thus creating a microenvironment favoring parasite proliferation. Despite lacking immunological memory, data in the literature suggest that, following initial stimulation, mononuclear phagocytes may become "trained" to respond more effectively to subsequent stimuli. Here we characterized the effects of macrophage sensitization using L. braziliensis exosomes prior to infection by the same pathogen. Human macrophages were stimulated with L. braziliensis exosomes and then infected with L. braziliensis. Higher levels of IL-1β and IL-6 were detected in cultures sensitized prior to infection compared to unstimulated infected cells. Moreover, stimulation with L. braziliensis exosomes induced macrophage production of IL-1β, IL-6, IL-10 and TNF. Inhibition of exosome secretion by L. braziliensis prior to macrophage infection reduced cytokine production and produced lower infection rates than untreated infected cells. Exosome stimulation also induced the consumption/regulation of NLRP3 inflammasome components in macrophages, while the blockade of NLRP3 resulted in lower levels of IL-6 and IL-1β. Our results suggest that L. braziliensis exosomes stimulate macrophages, leading to an exacerbated inflammatory state that may be NLRP3-dependent.

The Accuracy of Diagnosis and Genotyping of Leishmania Species Based on Spliced Leader Mini-Exon Gene by Nuclear Magnetic Resonance and Sequencing Assays

Background

We aimed to evaluate the accuracy of genotyping of Leishmania species by the spliced leader mini-exon gene.

Methods

Suspected leishmaniasis patients, referred to Masieh Daneshvary Hospital, Tehran, Iran were included from May 2017 to September 2021. The Leishmania species were genotyped by PCRRFLP based on the SL mini-exon gene and the ITS1 region of SSU-rRNA gene and compared with the sequencing results. The expressed metabolites of metacyclic promastigotes were evaluated by Proton nuclear magnetic resonance (1H-NMR).

Results

Out of 66 suspected cases, 36 (54.4%) were positive for Leishmania species based on the PCR assays. In 21 (31.8%) cases, promastigotes grew on culture tubes. Based on the RFLP of SL RNA profile, 13 (19.7%) L. tropica, 9 (13.6%) L. major, 3 (4.5%) L. infantum, and 8 (12.1%) C. fasciculata isolates, isolated from culture media, were identified; however, 3 (4.5%) cases were unidentifiable due to the low number of parasites. Seventeen metabolites were expressed by the metacyclic forms of L. major, L. tropica and C. fasciculata isolates. The top differential metabolites expressed more in C. fasciculata were FAD, p-Methoxybenzyl alcohol and S-b-G-5, 5-G-b-S (A = CH2) (P<0.005) whereas Veratryl glycerols and D-(+)-Mannose were significantly increased in L. major and Betulin, LTyrosine in L. tropica (P<0.01).

Conclusion

The invaluable techniques such as sequencing and 1H-NMR confirmed the results of genotyping of Leishmania species based on the SL mini-exon gene. SL mini exon gene can be used as a diagnostic tool to differentiate various Leishmania genotypes and detect contamination of culture media with C. fasciculata.

Transcriptional Shift and Metabolic Adaptations during Leishmania Quiescence Using Stationary Phase and Drug Pressure as Models

Microorganisms can adopt a quiescent physiological condition which acts as a survival strategy under unfavorable conditions. Quiescent cells are characterized by slow or non-proliferation and a deep downregulation of processes related to biosynthesis. Although quiescence has been described mostly in bacteria, this survival skill is widespread, including in eukaryotic microorganisms. In Leishmania, a digenetic parasitic protozoan that causes a major infectious disease, quiescence has been demonstrated, but the molecular and metabolic features enabling its maintenance are unknown. Here, we quantified the transcriptome and metabolome of Leishmania promastigotes and amastigotes where quiescence was induced in vitro either, through drug pressure or by stationary phase. Quiescent cells have a global and coordinated reduction in overall transcription, with levels dropping to as low as 0.4% of those in proliferating cells. However, a subset of transcripts did not follow this trend and were relatively upregulated in quiescent populations, including those encoding membrane components, such as amastins and GP63, or processes like autophagy. The metabolome followed a similar trend of overall downregulation albeit to a lesser magnitude than the transcriptome. It is noteworthy that among the commonly upregulated metabolites were those involved in carbon sources as an alternative to glucose. This first integrated two omics layers afford novel insight into cell regulation and show commonly modulated features across stimuli and stages.

Increased Leishmania infantum resistance to miltefosine and amphotericin B after treatment of a dog with miltefosine and allopurinol

Background

Leishmania infantum is the most important etiological agent of visceral leishmaniasis in the Americas and Mediterranean region, and the dog is the main host. Miltefosine was authorized to treat canine leishmaniasis (CanL) in Brazil in 2017, but there is a persistent fear of the emergence of parasites resistant not only to this drug but, through cross-resistance mechanisms, also to meglumine antimoniate and amphotericin B. Additionally, the literature shows that acquisition of resistance is followed by increased parasite fitness, with higher rates of proliferation, infectivity and metacyclogenesis, which are drivers of parasite virulence. In this context, the aim of this study was to analyze the impact of treating a dog with miltefosine and allopurinol on the generation of parasites resistant to miltefosine, amphotericin B and meglumine antimoniate.

Methods

In vitro susceptibility tests were conducted against miltefosine, amphotericin B and meglumine antimoniate with T0 (parasites isolated from a dog before treatment with miltefosine plus allopurinol), T1 (after 1 course of treatment) and T2 (after 2 courses of treatment) isolates. The rates of cell proliferation, infectivity and metacyclogenesis of the isolates were also evaluated.

Results

The results indicate a gradual increase in parasite resistance to miltefosine and amphotericin B with increasing the number of treatment courses. An increasing trend in the metacyclogenesis rate of the parasites was also observed as drug resistance increased.

Conclusion

The data indicates an increased L. infantum resistance to miltefosine and amphotericin B after the treatment of a dog with miltefosine plus allopurinol. Further studies with a larger number of L. infantum strains isolated from dogs with varied immune response profiles and undergoing different treatment regimes, are advocated.

Graphical Abstract

Involvement of Leishmania Phosphatases in Parasite Biology and Pathogeny

In the Leishmania lifecycle, the motile promastigote form is transmitted from the sand fly vector to a mammalian host during a blood meal. Inside vertebrate host macrophages, the parasites can differentiate into the amastigote form and multiply, causing leishmaniasis, one of the most significant neglected tropical diseases. Leishmania parasites face different conditions throughout their development inside sand flies. Once in the mammalian host, the parasites have to overcome the microbicide repertoire of the cells of the immune system to successfully establish the infection. In this context, the expression of protein phosphatases is of particular interest. Several members of the serine/threonine-specific protein phosphatase (STP), protein tyrosine phosphatase (PTP), and histidine acid phosphatase (HAcP) families have been described in different Leishmania species. Although their physiological roles have not been fully elucidated, many studies suggest they have an involvement with parasite biology and pathogeny. Phosphatases play a role in adaptation to nutrient starvation during parasite passage through the sand fly midgut. They are also important to parasite virulence, mainly due to the modulation of host cytokine production and impairment of the microbiocidal potential of macrophages. Furthermore, recent whole-genome expression analyses have shown that different phosphatases are upregulated in metacyclic promastigotes, the infective form of the mammalian host. Leishmania phosphatases are also upregulated in drug-resistant strains, probably due to the increase in drug efflux related to the activation of ABC transporters. Throughout this review, we will describe the physiological roles that have been attributed to Leishmania endogenous phosphatases, including their involvement in the adaptation, survival, and proliferation of the parasites inside their hosts.

Expression analysis of centrin gene in promastigote and amastigote forms of leishmania infantum iranian isolates: a promising target for live attenuated vaccine development against canine leishmaniasis

Background

Leishmania parasites express various essential proteins in different growth phases (logarithmic/stationary) and forms (promastigote/amastigote). Targeting the genes encoding such proteins paves the way for controlling these parasites. Centrin is an essential gene, which its protein product seems to be vital for the proliferation of Leishmania parasites. Herein, this study was contrived to analyze the expression level of the centrin gene in different growth phases and forms of Leishmania infantum (L. infantum) parasites isolated from various endemic areas of canine leishmaniasis (CanL) in Iran.

Results

All three collected isolates were identified as L. infantum using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Real-time reverse transcription (RT)-PCR revealed a statistically significant up-regulation (3.13-fold) in the logarithmic phase promastigotes compared to stationary ones (p < 0.01), whereas centrin was expressed equally in intracellular amastigotes at different time points during cell culture. Also, our finding revealed a slight up-regulation of the centrin gene (1.22-fold) in the intracellular amastigotes compared to logarithmic phase promastigotes, which was found statistically non-significant (p > 0.05).

Conclusions

Centrin gene in Iranian isolates of L. infantum is more expressed in exponential than stationary phases and seems to be considered as a promising target in the development of a genetically modified live attenuated vaccine for CanL control.

Evidence that a naturally occurring single nucleotide polymorphism in the RagC gene of Leishmania donovani contributes to reduced virulence

Leishmaniasis is a widespread neglected tropical disease transmitted by infected sand flies resulting in either benign cutaneous infection or fatal visceral disease. Leishmania donovani is the principal species responsible for visceral leishmaniasis, yet an atypical L. donovani has become attenuated in several countries including Sri Lanka and causes cutaneous leishmaniasis. Previous studies have identified 91 genes altered in the atypical cutaneous L. donovani compared to typical visceral disease associated L. donovani including mutations in the RagC and Raptor genes that are part of the eukaryotic conserved TOR pathway and its upstream sensing pathway. In the present study, we investigate whether the RagC R231C mutation present in atypical cutaneous L. donovani introduced into the virulent L. donovani 1S2D chromosome by CRISPR gene editing could affect virulence for survival in visceral organs. Through bioinformatic analysis, we further investigated the presence of sensing pathway components upstream of TOR in L. donovani including RagC complexing proteins, RagA and Raptor. L. donovani 1S2D edited to express mutant RagC R231C were viable in promastigote but had reduced visceral parasitemia in infected BALB/c mice. The RagC R231C mutant retained the ability to interact with RagA and gene knockout experiments revealed that although the RagA gene was essential, the RagC gene was not essential under promastigote culture conditions but was essential for survival in the liver of experimentally infected mice. These results provide evidence that the TOR associated sensing pathway plays a prominent role in L. donovani visceral disease and the RagC R231C mutation contributed to the atypical pathology of cutaneous L. donovani in Sri Lanka.

A Nuclear Magnetic Resonance-Based Metabolomic Study to Identify Metabolite Differences between Iranian Isolates of Leishmania major and Leishmania tropica

Background

Cutaneous leishmaniasis caused by Leishmania species (L. spp) is one of the most important parasitic diseases in humans. To gain information on the metabolite variations and biochemical pathways between L. spp, we used the comparative metabolome of metacyclic promastigotes in the Iranian isolates of L. major and L. tropica by proton nuclear magnetic resonance (¹H-NMR).

Methods

L. tropica and L. major were collected from three areas of Iran, namely Gonbad, Mashhad, and Bam, between 2017 and 2018, and were cultured. The metacyclic promastigote of each species was separated, and cell metabolites were extracted. ¹H-NMR spectroscopy was applied, and the data were processed using ProMatab in MATLAB (version 7.8.0.347). Multivariate statistical analyses, including the principal component analysis and the orthogonal projections to latent structures discriminant analysis, were performed to identify the discriminative metabolites between the two L. spp. Metabolites with variable influences in projection values of more than one and a P value of less than 0.05 were marked as significant differences.

Results

A set of metabolites were detected, and 24 significantly differentially expressed metabolites were found between the metacyclic forms of L. major and L. tropica isolates. The top differential metabolites were methionine, aspartate, betaine, and acetylcarnitine, which were increased more in L. tropica than L. major (P<0.005), whereas asparagine, 3-hydroxybutyrate, L-proline, and kynurenine were increased significantly in L. major (P<0.01). The significantly altered metabolites were involved in eight metabolic pathways.

Conclusion

Metabolomics, as an invaluable technique, yielded significant metabolites, and their biochemical pathways related to the metacyclic promastigotes of L. major and L. tropica. The findings offer greater insights into parasite biology and how pathogens adapt to their hosts.

The Phosphoenolpyruvate Carboxykinase Is a Key Metabolic Enzyme and Critical Virulence Factor of Leishmania major

There is currently no effective vaccine against leishmaniasis because of the lack of sufficient knowledge about the Ags that stimulate host-protective and long-lasting T cell-mediated immunity. We previously identified Leishmania phosphoenolpyruvate carboxykinase (PEPCK, a gluconeogenic enzyme) as an immunodominant Ag that is expressed by both the insect (promastigote) and mammalian (amastigote) stages of the parasite. In this study, we investigated the role of PEPCK in metabolism, virulence, and immunopathogenicity of Leishmania major We show that targeted loss of PEPCK results in impaired proliferation of L. major in axenic culture and bone marrow-derived macrophages. Furthermore, the deficiency of PEPCK results in highly attenuated pathology in vivo. BALB/c mice infected with PEPCK-deficient parasites failed to develop any cutaneous lesions despite harboring parasites at the cutaneous site of infection. This was associated with a dramatic reduction in the frequency of cytokine (IFN-γ, IL-4, and IL-10)-producing CD4⁺ T cells in spleens and lymph nodes draining the infection site. Cells from mice infected with PEPCK-deficient parasites also produced significantly low levels of these cytokines into the culture supernatant following in vitro restimulation with soluble Leishmania Ag. PEPCK-deficient parasites exhibited significantly greater extracellular acidification rate, increased proton leak, and decreased ATP-coupling efficiency and oxygen consumption rates in comparison with their wild-type and addback counterparts. Taken together, these results show that PEPCK is a critical metabolic enzyme for Leishmania, and its deletion results in altered metabolic activity and attenuation of virulence.

Functional genomics in sand fly-derived Leishmania promastigotes

Background

Leishmania development in the sand fly gut leads to highly infective forms called metacyclic promastigotes. This process can be routinely mimicked in culture. Gene expression–profiling studies by transcriptome analysis have been performed with the aim of studying promastigote forms in the sand fly gut, as well as differences between sand fly–and culture-derived promastigotes.

Findings

Transcriptome analysis has revealed the crucial role of the microenvironment in parasite development within the sand fly gut because substantial differences and moderate correlation between the transcriptomes of cultured and sand fly–derived promastigotes have been found. Sand fly–derived metacyclics are more infective than metacyclics in culture. Therefore, some caution should be exercised when using cultured promastigotes, depending on the experimental design. The most remarkable examples are the hydrophilic acidic surface protein/small endoplasmic reticulum protein (HASP/SHERP) cluster, the glycoprotein 63 (gp63), and autophagy genes, which are up-regulated in sand fly–derived promastigotes compared with cultured promastigotes. Because HASP/SHERP genes are up-regulated in nectomonad and metacyclic promastigotes in the sand fly, the encoded proteins are not metacyclic specific. Metacyclic promastigotes are distinguished by morphology and high infectivity. Isolating them from the sand fly gut is not exempt from technical difficulty, because other promastigote forms remain in the gut even 15 days after infection. Leishmania major procyclic promastigotes within the sand fly gut up-regulate genes involved in cell cycle regulation and glucose catabolism, whereas metacyclics increase transcript levels of fatty acid biosynthesis and ATP-coupled proton transport genes. Most parasite's signal transduction pathways remain uncharacterized. Future elucidation may improve understanding of parasite development, particularly signaling molecule-encoding genes in sand fly versus culture and between promastigote forms in the sand fly gut.

Conclusions

Transcriptome analysis has been demonstrated to be technically efficacious to study differential gene expression in sand fly gut promastigote forms. Transcript and protein levels are not well correlated in these organisms (approximately 25% quantitative coincidences), especially under stress situations and at differentiation processes. However, transcript and protein levels behave similarly in approximately 60% of cases from a qualitative point of view (increase, decrease, or no variation). Changes in translational efficiency observed in other trypanosomatids strongly suggest that the differences are due to translational regulation and regulation of the steady-state protein levels. The lack of low-input sample strategies does not allow translatome and proteome analysis of sand fly–derived promastigotes so far.

The contribution of DNA microarray technology to gene expression profiling in Leishmania spp.: A retrospective view

The first completed genome project of any living organism, excluding viruses, was of the gammaproteobacteria Haemophilus influenzae in 1995. Until the last decade, genome sequencing was very tedious because genome survey sequences (GSS) and/or expressed sequence tags (ESTs) belonging to plasmid, cosmid, and artificial chromosome genome libraries had to be sequenced and assembled in silico. No genome is completely assembled because gaps and unassembled contigs are always remaining. However, most represent an organism's whole genome from a practical point of view. The first genome sequencing projects of trypanosomatid parasites Leishmania major, Trypanosoma cruzi, and T. brucei were completed in 2005 following those strategies. The functional genomics era developed on the basis of microarray technology and has been continuously evolving. In the case of the genus Leishmania, substantial information about differentiation in the digenetic life cycle of the parasite has been obtained. More recently, next generation sequencing has revolutionized genome sequencing and functional genomics, leading to more sensitive and accurate results by using much fewer resources. Though this new technology is more advantageous, it does not invalidate microarray results. In fact, promising vaccine candidates and drug targets have been found by means of microarray-based screening and preliminary proof-of-concept tests.

Genome-wide identification of evolutionarily conserved Small Heat-Shock and eight other proteins bearing α-crystallin domain-like in kinetoplastid protists

Small Heat-Shock Proteins (sHSPs) and other proteins bearing alpha-crystallin domains (ACD) participate in defense against heat and oxidative stress and play important roles in cell cycle, cytoskeleton dynamics, and immunological and pathological mechanisms in eukaryotes. However, little is known about these proteins in early-diverging lineages of protists such as the kinetoplastids. Here, ACD-like proteins (ACDp) were investigated in genomes of 61 species of 12 kinetoplastid genera, including Trypanosoma spp. (23 species of mammals, reptiles and frogs), Leishmania spp. (mammals and lizards), trypanosomatids of insects, Phytomonas spp. of plants, and bodonids. Comparison of ACDps based on domain architecture, predicted tertiary structure, phylogeny and genome organization reveals a kinetoplastid evolutionarily conserved repertoire, which diversified prior to trypanosomatid adaptation to parasitic life. We identified 9 ACDp orthologs classified in 8 families of TryACD: four previously recognized (HSP20, Tryp23A, Tryp23B and ATOM69), and four characterized for the first time in kinetoplastids (TryACDP, TrySGT1, TryDYX1C1 and TryNudC). A single copy of each ortholog was identified in each genome alongside TryNudC1/TrypNudC2 homologs and, overall, ACDPs were under strong selection pressures at main phylogenetic lineages. Transcripts of all ACDPs were identified across the life stages of T. cruzi, T. brucei and Leishmania spp., but proteomic profiles suggested that most ACDPs may be species- and stage-regulated. Our findings establish the basis for functional studies, and provided evolutionary and structural support for an underestimated repertoire of ACDps in the kinetoplastids.

RNA-seq analysis reveals differences in transcript abundance between cultured and sand fly-derived Leishmania infantum promastigotes

Leishmania infantum is responsible for human and canine leishmaniasis in the Mediterranean basin, where the major vector is Phlebotomus perniciosus. Because isolation of sufficient parasites from the sand fly gut is technically challenging, axenic cultivation of promastigotes is routinely used to obtain material for biochemical and genetic analyses. Here, we report the use of Spliced Leader RNA-seq (SL-seq) to compare transcript abundance in cultured promastigotes and those obtained from the whole midgut of the sand fly 5 days after infection. SL-seq allows for amplification of RNA from the parasite avoiding contamination with RNA from the gut of the insect. The study has been performed by means of a single technical replicate comparing pools of samples obtained from sand fly-derived (sfPro) and axenic culture promastigotes (acPro). Although there was a moderate correlation (R² = 0.83) in gene expression, 793 genes showed significantly different (≥2-fold, p <0.05) mRNA levels in sand fly-derived promastigotes and in culture, of which 31 were up-regulated ≥8-fold (p < 10^-8 in most cases). These included several genes that are typically up-regulated during metacyclogenesis, suggesting that sand fly-derived promastigotes contain a substantial number of metacyclics, and/or that their differentiation status as metacyclics is more advanced in these populations. Infection experiments and studies evaluating the proportion of metacyclic promastigotes in culture and within the sand fly gut, previously reported by us, support the last hypothesis.

Increased miltefosine tolerance in clinical isolates of Leishmania donovani is associated with reduced drug accumulation, increased infectivity and resistance to oxidative stress

BACKGROUND

Miltefosine (MIL) is an oral antileishmanial drug used for treatment of visceral leishmaniasis (VL) in the Indian subcontinent. Recent reports indicate a significant decline in its efficacy with a high rate of relapse in VL as well as post kala-azar dermal leishmaniasis (PKDL). We investigated the parasitic factors apparently involved in miltefosine unresponsiveness in clinical isolates of Leishmania donovani.

METHODOLOGY

L. donovani isolated from patients of VL and PKDL at pretreatment stage (LdPreTx, n = 9), patients that relapsed after MIL treatment (LdRelapse, n = 7) and parasites made experimentally resistant to MIL (LdM30) were included in this study. MIL uptake was estimated using liquid chromatography coupled mass spectrometry. Reactive oxygen species and intracellular thiol content were measured fluorometrically. Q-PCR was used to assess the differential expression of genes associated with MIL resistance.

RESULTS

LdRelapse parasites exhibited higher IC50 both at promastigote level (7.92 ± 1.30 μM) and at intracellular amastigote level (11.35 ± 6.48 μM) when compared with LdPreTx parasites (3.27 ± 1.52 μM) and (3.85 ± 3.11 μM), respectively. The percent infectivity (72 hrs post infection) of LdRelapse parasites was significantly higher (80.71 ± 5.67%, P<0.001) in comparison to LdPreTx (60.44 ± 2.80%). MIL accumulation was significantly lower in LdRelapse parasites (1.7 fold, P<0.001) and in LdM30 parasites (2.4 fold, P<0.001) when compared with LdPreTx parasites. MIL induced ROS levels were significantly lower (p<0.05) in macrophages infected with LdRelapse while intracellular thiol content were significantly higher in LdRelapse compared to LdPreTx, indicating a better tolerance for oxidative stress in LdRelapse isolates. Genes associated with oxidative stress, metabolic processes and transporters showed modulated expression in LdRelapse and LdM30 parasites in comparison with LdPreTx parasites.

CONCLUSION

The present study highlights the parasitic factors and pathways responsible for miltefosine unresponsiveness in VL and PKDL.

In Vitro Inhibition of Leishmania Attachment to Sandfly Midguts and LL-5 Cells by Divalent Metal Chelators, Anti-gp63 and Phosphoglycans

Leishmania braziliensis and Leishmania infantum are the causative agents of cutaneous and visceral leishmaniasis, respectively. Several aspects of the vector-parasite interaction involving gp63 and phosphoglycans have been individually assayed in different studies. However, their role under the same experimental conditions was not studied yet. Here, the roles of divalent metal chelators, anti-gp63 antibodies and purified type I phosphoglycans (PGs) were evaluated during in vitro parasite attachment to the midgut of the vector. Parasites were treated with divalent metal chelators or anti-gp63 antibodies prior to the interaction with Lutzomyia longipalpis/Lutzomyia intermedia midguts or sand fly LL-5 cells. In vitro binding system was used to examine the role of PG and gp63 in parallel. Treatment with divalent metal chelators reduced Le. infantum adhesion to the Lu. longipalpis midguts. The most effective compound (Phen) inhibited the binding in both vectors. Similar results were observed in the interaction between both Leishmania species and the cell line LL-5. Finally, parallel experiments using anti-gp63-treated parasites and PG-incubated midguts demonstrated that both approaches substantially inhibited attachment in the natural parasite-vector pairs Le. infantum/Lu. longipalpis and Le. braziliensis/Lu. intermedia. Our results suggest that gp63 and/or PG are involved in parasite attachment to the midgut of these important vectors.