Leishmania (Viannia) braziliensis transfectants overexpressing the miniexon gene lose virulence in vivo

High Content Analysis of Macrophage-Targeting EhPIb-Compounds against Cutaneous and Visceral Leishmania Species

An immunostimulatory glycolipid molecule from the intestinal protozoan parasite Entamoeba histolytica (Eh) and its synthetic analogs derived from its phosphatidylinositol-b-anchor (EhPIb) previously showed considerable immunotherapeutic effects against Leishmania major infection in vitro and in vivo. Here, we describe a high content screening assay, based on primary murine macrophages. Parasites detection is based on a 90 kDA heat shock protein-specific staining, enabling the detection of several Leishmania species. We validated the assay using L. major, L. braziliensis, L. donovani, and L. infantum as well as investigated the anti-leishmanial activity of six immunostimulatory EhPIb-compounds (Eh-1 to Eh-6). Macrophages infected with dermotropic species were more sensitive towards treatment with the compounds as their viability showed a stronger reduction compared to macrophages infected with viscerotropic species. Most compounds caused a significant reduction of the infection rates and the parasite burdens depending on the infecting species. Only compound Eh-6 was found to have activity against all Leishmania species. Considering the challenges in anti-leishmanial drug discovery, we developed a multi-species screening assay capable of utilizing non-recombinant parasite strains, and demonstrated its usefulness by screening macrophage-targeting EhPIb-compounds showing their potential for the treatment of cutaneous and visceral leishmaniasis.

Application of CRISPR/Cas9-Based Reverse Genetics in Leishmania braziliensis: Conserved Roles for HSP100 and HSP23

The protozoan parasite Leishmania (Viannia) braziliensis (L. braziliensis) is the main cause of human tegumentary leishmaniasis in the New World, a disease affecting the skin and/or mucosal tissues. Despite its importance, the study of the unique biology of L. braziliensis through reverse genetics analyses has so far lagged behind in comparison with Old World Leishmania spp. In this study, we successfully applied a cloning-free, PCR-based CRISPR–Cas9 technology in L. braziliensis that was previously developed for Old World Leishmania major and New World L. mexicana species. As proof of principle, we demonstrate the targeted replacement of a transgene (eGFP) and two L. braziliensis single-copy genes (HSP23 and HSP100). We obtained homozygous Cas9-free HSP23- and HSP100-null mutants in L. braziliensis that matched the phenotypes reported previously for the respective L. donovani null mutants. The function of HSP23 is indeed conserved throughout the Trypanosomatida as L. majorHSP23 null mutants could be complemented phenotypically with transgenes from a range of trypanosomatids. In summary, the feasibility of genetic manipulation of L. braziliensis by CRISPR–Cas9-mediated gene editing sets the stage for testing the role of specific genes in that parasite’s biology, including functional studies of virulence factors in relevant animal models to reveal novel therapeutic targets to combat American tegumentary leishmaniasis.

Reverse Epidemiology: An Experimental Framework to Drive Leishmania Biomarker Discovery in situ by Functional Genetic Screening Using Relevant Animal Models

Leishmania biomarker discovery remains an important challenge that needs to be revisited in light of our increasing knowledge on parasite-specific biology, notably its genome instability. In the absence of classical transcriptional regulation in these early-branching eukaryotes, fluctuations in transcript abundance can be generated by gene and chromosome amplifications, which have been linked to parasite phenotypic variability with respect to virulence, tissue tropism, and drug resistance. Conducting in vitro evolutionary experiments to study mechanisms of Leishmania environmental adaptation, we recently validated the link between parasite genetic amplification and fitness gain, thus defining gene and chromosome copy number variations (CNVs) as important Leishmania biomarkers. These experiments also demonstrated that long-term Leishmania culture adaptation can strongly interfere with epidemiologically relevant, genetic signals, which challenges current protocols for biomarker discovery, all of which rely on in vitro expansion of clinical isolates. Here we propose an experimental framework independent of long-term culture termed “reverse” epidemiology, which applies established protocols for functional genetic screening of cosmid-transfected parasites in animal models for the identification of clinically relevant genetic loci that then inform targeted field studies for their validation as Leishmania biomarkers.

Development of an automated image analysis protocol for quantification of intracellular forms of Leishmania spp

Leishmania parasites cause a set of neglected tropical diseases with considerable public health impact, the leishmaniases, which are often fatal if left untreated. Since current treatments for the leishmaniases exhibit high toxicity, low efficacy and prohibitive prices, many laboratories throughout the world are engaged in research for the discovery of novel chemotherapeutics. This entails the necessity of screening large numbers of compounds against the clinically relevant form of the parasite, the obligatory intracellular amastigote, a procedure that in many laboratories is still carried out by manual inspection. To overcome this well-known bottleneck in Leishmania drug development, several studies have recently attempted to automate this process. Here we implemented an image-based high content triage assay for Leishmania which has the added advantages of using primary macrophages instead of macrophage cell lines and of enabling identification of active compounds against parasite species developing both in small individual phagolysosomes (such as L. infantum) and in large communal vacuoles (such as L. amazonensis). The automated image analysis protocol is made available for IN Cell Analyzer systems, and, importantly, also for the open-source CellProfiler software, in this way extending its implementation to any laboratory involved in drug development as well as in other aspects of Leishmania research requiring analysis of in vitro infected macrophages.

Differential Gene Expression and Infection Profiles of Cutaneous and Mucosal Leishmania braziliensis Isolates from the Same Patient

Background

Leishmaniasis is a complex disease in which clinical outcome depends on factors such as parasite species, host genetics and immunity and vector species. In Brazil, Leishmania (Viannia) braziliensis is a major etiological agent of cutaneous (CL) and mucosal leishmaniasis (MCL), a disfiguring form of the disease, which occurs in ~10% of L. braziliensis-infected patients. Thus, clinical isolates from patients with CL and MCL may be a relevant source of information to uncover parasite factors contributing to pathogenesis. In this study, we investigated two pairs of L. (V.) braziliensis isolates from mucosal (LbrM) and cutaneous (LbrC) sites of the same patient to identify factors distinguishing parasites that migrate from those that remain at the primary site of infection.

Methodology/Principal Findings

We observed no major genomic divergences among the clinical isolates by molecular karyotype and genomic sequencing. RT-PCR revealed that the isolates lacked Leishmania RNA virus (LRV). However, the isolates exhibited distinct in vivo pathogenesis in BALB/c mice; the LbrC isolates were more virulent than the LbrM isolates. Metabolomic analysis revealed significantly increased levels of 14 metabolites in LbrC parasites and 31 metabolites in LbrM parasites that were mainly related to inflammation and chemotaxis. A proteome comparative analysis revealed the overexpression of LbrPGF2S (prostaglandin f2-alpha synthase) and HSP70 in both LbrC isolates. Overexpression of LbrPGF2S in LbrC and LbrM promastigotes led to an increase in infected macrophages and the number of amastigotes per cell at 24–48 h post-infection (p.i.).

Conclusions/Significance

Despite sharing high similarity at the genome structure and ploidy levels, the parasites exhibited divergent expressed genomes. The proteome and metabolome results indicated differential profiles between the cutaneous and mucosal isolates, primarily related to inflammation and chemotaxis. BALB/c infection revealed that the cutaneous isolates were more virulent than the mucosal parasites. Furthermore, our data suggest that the LbrPGF2S protein is a candidate to contribute to parasite virulence profiles in the mammalian host.

Leishmaniasis is a critical public health problem worldwide. The clinical outcome of leishmaniasis depends on the infecting parasite species, host genetics and immune response and insect species. Leishmania braziliensis is a major etiological agent of cutaneous and mucosal leishmaniasis in Brazil. Fewer than 10% of L. braziliensis-infected patients with CL develop the mucosal form (a severe clinical manifestation). The small number of parasites in the mucosae increases the difficulty of obtaining clinical isolates, and parasite samples are frequently derived from individuals with different genetic backgrounds. Therefore, clinical isolates from cutaneous and mucosal sites from the same patient represent unique tools to understand parasite factors that contribute to disease outcome and pathogenesis. In this study, we investigated parasite factors involved in disease progression using two pairs of L. (V.) braziliensis isolates from mucosal (LbrM) and cutaneous (LbrC) sites of the same patient. In conclusion, the murine infection and proteome and metabolome data suggest that the differences between the cutaneous and mucosal isolates are mainly related to inflammation and chemotaxis. Our data also suggest that the LbrPGF2S protein plays a role in parasite virulence in the mammalian host.

An image-based high-content screening assay for compounds targeting intracellular Leishmania donovani amastigotes in human macrophages

Leishmaniasis is a tropical disease threatening 350 million people from endemic regions. The available drugs for treatment are inadequate, with limitations such as serious side effects, parasite resistance or high cost. Driven by this need for new drugs, we developed a high-content, high-throughput image-based screening assay targeting the intracellular amastigote stage of different species of Leishmania in infected human macrophages. The in vitro infection protocol was adapted to a 384-well-plate format, enabling acquisition of a large amount of readouts by automated confocal microscopy. The reading method was based on DNA staining and required the development of a customized algorithm to analyze the images, which enabled the use of non-modified parasites. The automated analysis generated parameters used to quantify compound activity, including infection ratio as well as the number of intracellular amastigote parasites and yielded cytotoxicity information based on the number of host cells. Comparison of this assay with one that used the promastigote form to screen 26,500 compounds showed that 50% of the hits selected against the intracellular amastigote were not selected in the promastigote screening. These data corroborate the idea that the intracellular amastigote form of the parasite is the most appropriate to be used in primary screening assay for Leishmania.

Cell homeostasis in a Leishmania major mutant overexpressing the spliced leader RNA is maintained by an increased proteolytic activity

Although several stage-specific genes have been identified in Leishmania, the molecular mechanisms governing developmental gene regulation in this organism are still not well understood. We have previously reported an attenuation of virulence in Leishmania major and L. braziliensis carrying extra-copies of the spliced leader RNA gene. Here, we surveyed the major differences in proteome and transcript expression profiles between the spliced leader RNA overexpressor and control lines using two-dimensional gel electrophoresis and differential display reverse transcription PCR, respectively. Thirty-nine genes related to stress response, cytoskeleton, proteolysis, cell cycle control and proliferation, energy generation, gene transcription, RNA processing and post-transcriptional regulation have abnormal patterns of expression in the spliced leader RNA overexpressor line. The evaluation of proteolytic pathways in the mutant revealed a selective increase of cysteine protease activity and an exacerbated ubiquitin-labeled protein population. Polysome profile analysis and measurement of cellular protein aggregates showed that protein translation in the spliced leader RNA overexpressor line is increased when compared to the control line. We found that L. major promastigotes maintain homeostasis in culture when challenged with a metabolic imbalance generated by spliced leader RNA surplus through modulation of intracellular proteolysis. However, this might interfere with a fine-tuned gene expression control necessary for the amastigote multiplication in the mammalian host.