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

Novel thiosemicarbazones of coumarin incorporated isatins: synthesis, structural characterization and antileishmanial activity

Leishmaniasis, a neglected tropical disease affecting 0.7 to 1.3 million people annually, has only a few toxic therapeutic options. This study describes the synthesis, structural characterization, in silico and in vitro assessment of novel thiosemicarbazones of coumarin incorporated isatins (6a-6m) as highly as potent and safe antileishmanial agents. Molecular docking was initially used to determine the binding of these compounds to the active cavity of the target protein (Leishmanolysin gp63) of Leishmania (L.) tropica. Among all the docked compounds, three 6d, 6f and 6l showed high binding affinities due to strong H-bonds and hydrophobic π-interactions. Importantly, the in vitro investigations of thirteen synthesized compounds for antileishmanial activity against L. tropica promastigotes and axenic amastigotes, complemented the docking results. The compound 6d was found to be the most active of the series at micromolar concentrations both against promastigotes (IC50 = 2.985 μmol/L) and axenic amastigotes (IC50 = 13.46 μmol/L) in comparison to the tarter emetic (IC50 = 12.56 μmol/L) and amphotericin B (IC50 = 1.826 μmol/L), respectively. Significantly, all active compounds are much less toxic as compared to the positive control (Triton X-100) and, tartar emetic (TA) and amphotericin B when screened for their toxicity against human erythrocytes. To gain further insight into the interaction dynamics of our target protein on binding with compound 6d, molecular dynamic simulation was performed for a course of 100 ns for both the apo-protein and the protein-ligand complex. The results revealed consistent structural stability for the protein-ligand complex, aligning with characteristics seen in the apo-proteins.

Ubiquitin Ligases in Control: Regulating NLRP3 Inflammasome Activation

Ubiquitin ligases play pivotal roles in the regulation of NLR family pyrin domain containing 3 (NLRP3) inflammasome activation, a critical process in innate immunity and inflammatory responses. This review explores the intricate mechanisms by which various E3 ubiquitin ligases exert both positive and negative influences on NLRP3 inflammasome activity through diverse post-translational modifications. Negative regulation of NLRP3 inflammasome assembly is mediated by several E3 ligases, including F-box and leucine-rich repeat protein 2 (FBXL2), tripartite motif-containing protein 31 (TRIM31), and Casitas B-lineage lymphoma b (Cbl-b), which induce K48-linked ubiquitination of NLRP3, targeting it for proteasomal degradation. Membrane-associated RING-CH 7 (MARCH7) similarly promotes K48-linked ubiquitination leading to autophagic degradation, while RING finger protein (RNF125) induces K63-linked ubiquitination to modulate NLRP3 function. Ariadne homolog 2 (ARIH2) targets the nucleotide-binding domain (NBD) domain of NLRP3, inhibiting its activation, and tripartite motif-containing protein (TRIM65) employs dual K48 and K63-linked ubiquitination to suppress inflammasome assembly. Conversely, Pellino2 exemplifies a positive regulator, promoting NLRP3 inflammasome activation through K63-linked ubiquitination. Additionally, ubiquitin ligases influence other components critical for inflammasome function. TNF receptor-associated factor 3 (TRAF3) mediates K63 polyubiquitination of apoptosis-associated speck-like protein containing a CARD (ASC), facilitating its degradation, while E3 ligases regulate caspase-1 activation and DEAH-box helicase 33 (DHX33)-NLRP3 complex formation through specific ubiquitination events. Beyond direct inflammasome regulation, ubiquitin ligases impact broader innate immune signaling pathways, modulating pattern-recognition receptor responses and dendritic cell maturation. Furthermore, they intricately control NOD1/NOD2 signaling through K63-linked polyubiquitination of receptor-interacting protein 2 (RIP2), crucial for nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and mitogen-activated protein kinase (MAPK) activation. Furthermore, we explore how various pathogens, including bacteria, viruses, and parasites, have evolved sophisticated strategies to hijack the host ubiquitination machinery, manipulating NLRP3 inflammasome activation to evade immune responses. This comprehensive analysis provides insights into the molecular mechanisms underlying inflammasome regulation and their implications for inflammatory diseases, offering potential avenues for therapeutic interventions targeting the NLRP3 inflammasome. In conclusion, ubiquitin ligases emerge as key regulators of NLRP3 inflammasome activation, exhibiting a complex array of functions that finely tune immune responses. Understanding these regulatory mechanisms not only sheds light on fundamental aspects of inflammation but also offers potential therapeutic avenues for inflammatory disorders and infectious diseases.

VAPA mediates lipid exchange between Leishmania amazonensis and host macrophages

Leishmania is a vacuolar pathogen that replicates within parasitophorous vacuoles inside host phagocytes. To promote its replication, Leishmania relies on a panoply of strategies to acquire macromolecules such as lipids from host macrophages. In this study, we have evaluated the role of VAPA, an endoplasmic reticulum-resident membrane protein involved in inter-organellar lipid transport, in macrophages infected with L. amazonensis. Following infection of bone marrow-derived macrophages with L. amazonensis metacyclic promastigotes, we observed that VAPA gradually associates with communal parasitophorous vacuoles. Knockdown of VAPA prevented the replication of L. amazonensis, which was accompanied by an impaired parasitophorous vacuole expansion. Using fluorescent ceramide, we established that VAPA is required for the transport of sphingolipids to the parasitophorous vacuoles and for its acquisition by L. amazonensis amastigotes. Proximity-ligation assays revealed that L. amazonensis hijacks VAPA by disrupting its interactions with the host cell lipid transfer proteins CERT and ORP1L. Finally, we found that VAPA is essential for the transfer of the Leishmania virulence glycolipid lipophosphoglycan from the parasitophorous vacuoles to the host cell endoplasmic reticulum. We propose that VAPA contributes to the ability of L. amazonensis to colonize macrophages by mediating bi-directional transfer of lipids essential for parasite replication and virulence between the parasitophorous vacuoles and the host cell endoplasmic reticulum.

Immunomodulation by Leishmania parasites: Potential for controlling other diseases

In the mammalian hosts, Leishmania parasites survive and proliferate within phagolysosomes of macrophages. To avoid being killed by the immune cells, Leishmania parasites utilize their molecules to manipulate macrophages' functions for survival. Targets of such immunomodulatory molecules are not limited to macrophages, as Leishmania-derived molecules sometimes show influence on other immune cells such as neutrophils, dendritic cells, T cells and B cells. This review covers research on immunomodulation of host immunity by Leishmania parasites and introduces some examples of parasite-derived molecules participating in the immunomodulation. For example, Leishmania cell surface lipophosphoglycan (LPG) can modulate TLR2 signaling and PI3K/Akt axis in macrophages leading to induction of Th2 cells. Because chronic secretion of inflammatory cytokines is one of the causes of immune-mediated diseases such as atherosclerosis, Crohn's disease, and rheumatoid arthritis, LPG may be useful as a drug to suppress the inflammatory conditions. The unique characteristics of leishmanial molecules pose a promise as a source of immunomodulatory drugs for controlling diseases other than leishmaniasis.

Leishmania amazonensis-derived extracellular vesicles (EVs) induce neutrophil extracellular traps (NETs)

Neutrophils interact with Leishmania when the sandfly vector inoculates these parasites in the host with saliva and promastigotes-derived extracellular vesicles (EVs). It has been shown that this co-injection induces inflammation and exacerbates leishmaniasis lesions. EVs are a heterogeneous group of vesicles released by cells that play a crucial role in intercellular communication. Neutrophils are among the first cells to interact with the parasites and release neutrophil extracellular traps (NETs) that ensnare and kill the promastigotes. Here, we show that Leishmania amazonensis EVs induce NET formation and identify molecular mechanisms involved. We showed the requirement of neutrophils' toll-like receptors for EVs-induced NET. EVs carrying the virulence factors lipophosphoglycan and the zinc metalloproteases were endocytosed by some neutrophils and snared by NETs. EVs-induced NET formation required reactive oxygen species, myeloperoxidase, elastase, peptidyl arginine deiminase, and Ca++. The proteomic analysis of the EVs cargo revealed 1,189 proteins; the 100 most abundant identified comprised some known Leishmania virulent factors. Importantly, L. amazonensis EVs-induced NETs lead to the killing of promastigotes and could participate in the exacerbated inflammatory response induced by the EVs, which may play a role in the pathogenesis process.

Metalloenzyme Inhibitors against Zoonotic Infections: Focus on Leishmania and Schistosoma

The term "zoonosis" denotes diseases transmissible among vertebrate animals and humans. These diseases constitute a significant public health challenge, comprising 61% of human pathogens and causing an estimated 2.7 million deaths annually. Zoonoses not only affect human health but also impact animal welfare and economic stability, particularly in low- and middle-income nations. Leishmaniasis and schistosomiasis are two important neglected tropical diseases with a high prevalence in tropical and subtropical areas, imposing significant burdens on affected regions. Schistosomiasis, particularly rampant in sub-Saharan Africa, lacks alternative treatments to praziquantel, prompting concerns regarding parasite resistance. Similarly, leishmaniasis poses challenges with unsatisfactory treatments, urging the development of novel therapeutic strategies. Effective prevention demands a One Health approach, integrating diverse disciplines to enhance diagnostics and develop safer drugs. Metalloenzymes, involved in parasite biology and critical in different biological pathways, emerged in the last few years as useful drug targets for the treatment of human diseases. Herein we have reviewed recent reports on the discovery of inhibitors of metalloenzymes associated with zoonotic diseases like histone deacetylases (HDACs), carbonic anhydrase (CA), arginase, and heme-dependent enzymes.

Immunomodulatory properties of Leishmania tarentolae extracellular vesicles containing the Spike protein of SARS-CoV-2

Extracellular vesicles released by the protozoan parasite Leishmania display immunomodulatory properties towards mammalian immune cells. In this study, we have evaluated the potential of extracellular vesicles derived from the non-pathogenic protozoan Leishmania tarentolae towards the development of a vaccine adjuvant. As a proof of concept, we expressed in L. tarentolae a codon-optimized SARS-CoV-2 Spike protein fused to the L. mexicana secreted acid phosphatase signal peptide in the N-terminal and to a 6×-His stretch in the C-terminal. Extracellular vesicles released by the engineered L. tarentolae were isolated by ultracentrifugation and fast protein liquid chromatography and were characterized via nanoparticle tracking analysis and transmission electron microscopy. The recombinant S protein was present in extracellular vesicles released by L. tarentolae, as determined by Western blot analyses and immunoelectron microscopy. Next, we evaluated the immunomodulatory potential of extracellular vesicles containing the S protein towards bone-marrow-derived macrophages and bone-marrow-derived dendritic cells. Our data show that in bone-marrow-derived dendritic cells, extracellular vesicles containing the S protein induced an increased expression of proinflammatory genes compared to plain extracellular vesicles whereas the opposite was observed in bone-marrow-derived macrophages. These findings reveal the immunomodulatory potential of L. tarentolae extracellular vesicles and provide a proof of concept that they can be used as adjuvant in the context of dendritic cell stimulation.

The protein map of the protozoan parasite Leishmania (Leishmania) amazonensis, Leishmania (Viannia) braziliensis and Leishmania (Leishmania) infantum during growth phase transition and temperature stress

Leishmania parasites cause a spectrum of diseases termed leishmaniasis, which manifests in two main clinical forms, cutaneous and visceral leishmaniasis. Leishmania promastigotes transit from proliferative exponential to quiescent stationary phases inside the insect vector, a relevant step that recapitulates early molecular events of metacyclogenesis. During the insect blood meal of the mammalian hosts, the released parasites interact initially with the skin, an event marked by temperature changes. Deep knowledge on the molecular events activated during Leishmania-host interactions in each step is crucial to develop better therapies and to understand the pathogenesis. In this study, the proteomes of Leishmania (Leishmania) amazonensis (La), Leishmania (Viannia) braziliensis (Lb), and Leishmania (Leishmania) infantum (syn L. L. chagasi) (Lc) were analyzed using quantitative proteomics to uncover the proteome modulation in three different conditions related to growth phases and temperature shifts: 1) exponential phase (Exp); 2) stationary phase (Sta25) and; 3) stationary phase subjected to heat stress (Sta34). Functional validations were performed using orthogonal techniques, focusing on α-tubulin, gp63 and heat shock proteins (HSPs). Species-specific and condition-specific modulation highlights the plasticity of the Leishmania proteome, showing that pathways related to metabolism and cytoskeleton are significantly modulated from exponential to stationary growth phases, while protein folding, unfolded protein binding, signaling and microtubule-based movement were differentially altered during temperature shifts. This study provides an in-depth proteome analysis of three Leishmania spp., and contributes compelling evidence of the molecular alterations of these parasites in conditions mimicking the interaction of the parasites with the insect vector and vertebrate hosts. SIGNIFICANCE: Leishmaniasis disease manifests in two main clinical forms according to the infecting Leishmania species and host immune responses, cutaneous and visceral leishmaniasis. In Brazil, cutaneous leishmaniasis (CL) is associated with L. braziliensis and L. amazonensis, while visceral leishmaniasis, also called kala-azar, is caused by L. infantum. Leishmania parasites remodel their proteomes during growth phase transition and changes in their mileu imposed by the host, including temperature. In this study, we performed a quantitative mass spectrometry-based proteomics to compare the proteome of three New world Leishmania species, L. amazonensis (La), L. braziliensis (Lb) and L. infantum (syn L. chagasi) (Lc) in three conditions: a) exponential phase at 25 °C (Exp); b) stationary phase at 25 °C (Sta25) and; c) stationary phase subjected to temperature stress at 34 °C (Sta34). This study provides an in-depth proteome analysis of three Leishmania spp. with varying pathophysiological outcomes, and contributes compelling evidence of the molecular alterations of these parasites in conditions mimicking the interaction of the parasites with the insect vector and vertebrate hosts.

Immunogenicity and Neutralization Potential of Recombinant Chimeric Protein Comprising the Catalytic Region of Gp63 of Leishmania and LTB against Leishmania donovani

AIM

To study the inhibition potential of antibody against a recombinant chimera comprising of the catalytic epitope of gp63 of Leishmania donovani and B subunit of heat-labile enterotoxin (LTB) in the functional activity of L. donovani.

BACKGROUND

Visceral leishmaniasis, caused by the protozoan parasite Leishmania donovani, is a major health problem and causes mortality in tropical regions. Protozoan proteases play a crucial role in the pathogenesis of the disease and in establishing infection by countering the host's innate immune responses, namely complement-mediated lysis and phagocytosis. A surface-bound metalloprotease (gp63) has been reported to be a major virulence factor resulting in the evasion of complement- mediated lysis, cleaving host extracellular and intracellular substrates, resulting in intra- phagolysosomal survival.

METHODS

The epitope corresponding to the catalytic motif of gp63 of Leishmania donovani was fused with the B subunit of heat-labile enterotoxin, which is known to be immunogenic. The chimera was cloned to a prokaryotic expression vector and purified using Ni NTA affinity chromatography. Antibodies were generated against the purified fusion protein and analyzed for its ability to bind to the gp63 catalytic motif peptide by ELISA. The effect of fusion protein antibody on the functional activity of gp63 was evaluated by assessing the effect of purified IgGs on the protease activity and complement-mediated lysis of L. donovani promastigotes in vitro.

RESULTS

The present study reports that a recombinant chimera of the catalytic epitope of gp63 and B subunit of heat-labile enterotoxin (LTB) of E. coli, a potent adjuvant of humoral response can mount significant immune response towards the catalytic epitope. ELISA and Western blot analysis showed that the anti-fusion protein antiserum could recognize the native gp63. Also, it significantly inhibited the protease activity of promastigotes and subsequently increased complement-mediated lysis of the promastigotes in vitro.

CONCLUSION

It could be concluded that the hybrid protein containing catalytic motif L. donovani gp63 protein and carrier protein (LTB) could elicit antibodies that could neutralise the functional activity of gp63 and thus could be a potential candidate for subunit leishmaniasis vaccine.

LeishMANIAdb: a comparative resource for Leishmania proteins

Leishmaniasis is a detrimental disease causing serious changes in quality of life and some forms can lead to death. The disease is spread by the parasite Leishmania transmitted by sandfly vectors and their primary hosts are vertebrates including humans. The pathogen penetrates host cells and secretes proteins (the secretome) to repurpose cells for pathogen growth and to alter cell signaling via host-pathogen protein-protein interactions). Here, we present LeishMANIAdb, a database specifically designed to investigate how Leishmania virulence factors may interfere with host proteins. Since the secretomes of different Leishmania species are only partially characterized, we collated various experimental evidence and used computational predictions to identify Leishmania secreted proteins to generate a user-friendly unified web resource allowing users to access all information available on experimental and predicted secretomes. In addition, we manually annotated host-pathogen interactions of 211 proteins and the localization/function of 3764 transmembrane (TM) proteins of different Leishmania species. We also enriched all proteins with automatic structural and functional predictions that can provide new insights in the molecular mechanisms of infection. Our database may provide novel insights into Leishmania host-pathogen interactions and help to identify new therapeutic targets for this neglected disease. Database URL  https://leishmaniadb.ttk.hu/.

Evolutionary, structural and functional insights in nuclear organisation and nucleocytoplasmic transport in trypanosomes

One of the remarkable features of eukaryotes is the nucleus, delimited by the nuclear envelope (NE), a complex structure and home to the nuclear lamina and nuclear pore complex (NPC). For decades, these structures were believed to be mainly architectural elements and, in the case of the NPC, simply facilitating nucleocytoplasmic trafficking. More recently, the critical roles of the lamina, NPC and other NE constituents in genome organisation, maintaining chromosomal domains and regulating gene expression have been recognised. Importantly, mutations in genes encoding lamina and NPC components lead to pathogenesis in humans, while pathogenic protozoa disrupt the progression of normal development and expression of pathogenesis-related genes. Here, we review features of the lamina and NPC across eukaryotes and discuss how these elements are structured in trypanosomes, protozoa of high medical and veterinary importance, highlighting lineage-specific and conserved aspects of nuclear organisation.

Potential protective effects of Huanglian Jiedu Decoction against COVID-19-associated acute kidney injury: A network-based pharmacological and molecular docking study

Corona virus disease 2019 (COVID-19) is prone to induce multiple organ damage. The kidney is one of the target organs of SARS-CoV-2, which is susceptible to inducing acute kidney injury (AKI). Huanglian Jiedu Decoction (HLJDD) is one of the recommended prescriptions for COVID-19 with severe complications. We used network pharmacology and molecular docking to explore the therapeutic and protective effects of HLJDD on COVID-19-associated AKI. Potential targets related to "HLJDD," "COVID-19," and "Acute Kidney Injury/Acute Renal Failure" were identified from several databases. A protein-protein interaction (PPI) network was constructed and screened the core targets according to the degree value. The target genes were then enriched using gene ontology and Kyoto Encyclopedia of Genes and Genomes. The bioactive components were docked with the core targets. A total of 65 active compounds, 85 common targets for diseases and drugs were obtained; PPI network analysis showed that the core protein mainly involved JUN, RELA, and AKT1; functional analysis showed that these target genes were mainly involved in lipid and atherosclerosis signaling pathway and IL-17 signal pathway. The results of molecular docking showed that JUN, RELA, and AKT1 had good binding activity with the effective chemical components of HLJDD. In conclusion, HLJDD can be used as a potential therapeutic drug for COVID-19-associated AKI.

Ethanolaminephosphate cytidylyltransferase is essential for survival, lipid homeostasis and stress tolerance in Leishmania major

Glycerophospholipids including phosphatidylethanolamine (PE) and phosphatidylcholine (PC) are vital components of biological membranes. Trypanosomatid parasites of the genus Leishmania can acquire PE and PC via de novo synthesis and the uptake/remodeling of host lipids. In this study, we investigated the ethanolaminephosphate cytidylyltransferase (EPCT) in Leishmania major, which is the causative agent for cutaneous leishmaniasis. EPCT is a key enzyme in the ethanolamine branch of the Kennedy pathway which is responsible for the de novo synthesis of PE. Our results demonstrate that L. major EPCT is a cytosolic protein capable of catalyzing the formation of CDP-ethanolamine from ethanolamine-phosphate and cytidine triphosphate. Genetic manipulation experiments indicate that EPCT is essential in both the promastigote and amastigote stages of L. major as the chromosomal null mutants cannot survive without the episomal expression of EPCT. This differs from our previous findings on the choline branch of the Kennedy pathway (responsible for PC synthesis) which is required only in promastigotes but not amastigotes. While episomal EPCT expression does not affect promastigote proliferation under normal conditions, it leads to reduced production of ethanolamine plasmalogen or plasmenylethanolamine, the dominant PE subtype in Leishmania. In addition, parasites with episomal EPCT exhibit heightened sensitivity to acidic pH and starvation stress, and significant reduction in virulence. In summary, our investigation demonstrates that proper regulation of EPCT expression is crucial for PE synthesis, stress response, and survival of Leishmania parasites throughout their life cycle.

Ethanolaminephosphate cytidyltransferase is essential for survival, lipid homeostasis and stress tolerance in Leishmania major

Glycerophospholipids including phosphatidylethanolamine (PE) and phosphatidylcholine (PC) are vital components of biological membranes. Trypanosomatid parasites of the genus Leishmania can acquire PE and PC via de novo synthesis and the uptake/remodeling of host lipids. In this study, we investigated the ethanolaminephosphate cytidyltransferase (EPCT) in Leishmania major , which is the causative agent for cutaneous leishmaniasis. EPCT is a key enzyme in the ethanolamine branch of the Kennedy pathway which is responsible for the de novo synthesis of PE. Our results demonstrate that L. major EPCT is a cytosolic protein capable of catalyzing the formation of CDP-ethanolamine from ethanolamine-phosphate and cytidine triphosphate. Genetic manipulation experiments indicate that EPCT is essential in both the promastigote and amastigote stages of L. major as the chromosomal null mutants cannot survive without the episomal expression of EPCT. This differs from our previous findings on the choline branch of the Kennedy pathway (responsible for PC synthesis) which is required only in promastigotes but not amastigotes. While episomal EPCT expression does not affect promastigote proliferation under normal conditions, it leads to reduced production of ethanolamine plasmalogen or plasmenylethanolamine, the dominant PE subtype in Leishmania . In addition, parasites with epsiomal EPCT exhibit heightened sensitivity to acidic pH and starvation stress, and significant reduction in virulence. In summary, our investigation demonstrates that proper regulation of EPCT expression is crucial for PE synthesis, stress response, and survival of Leishmania parasites throughout their life cycle.

AUTHOR SUMMARY

In nature, Leishmania parasites alternate between fast replicating, extracellular promastigotes in sand fly gut and slow growing, intracellular amastigotes in macrophages. Previous studies suggest that promastigotes acquire most of their lipids via de novo synthesis whereas amastigotes rely on the uptake and remodeling of host lipids. Here we investigated the function of ethanolaminephosphate cytidyltransferase (EPCT) which catalyzes a key step in the de novo synthesis of phosphatidylethanolamine (PE) in Leishmania major . Results showed that EPCT is indispensable for both promastigotes and amastigotes, indicating that de novo PE synthesis is still needed at certain capacity for the intracellular form of Leishmania parasites. In addition, elevated EPCT expression alters overall PE synthesis and compromises parasite’s tolerance to adverse conditions and is deleterious to the growth of intracellular amastigotes. These findings provide new insight into how Leishmania acquire essential phospholipids and how disturbance of lipid metabolism can impact parasite fitness.