Leishmania lipophosphoglycan activates the transcription factor activating protein 1 in J774A.1 macrophages through the extracellular signal-related kinase (ERK) and p38 mitogen-activated protein kinase

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

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

Leishmania donovani Secretory Mevalonate Kinase Regulates Host Immune Response and Facilitates Phagocytosis

Leishmania secretes over 151 proteins during in vitro cultivation. Cellular functions of one such novel protein: mevalonate kinase is discussed here; signifying its importance in Leishmania infection.

Visceral Leishmaniasis is a persistent infection, caused by Leishmania donovani in Indian subcontinent. This persistence is partly due to phagocytosis and evasion of host immune response. The underlying mechanism involves secretory proteins of Leishmania parasite; however, related studies are meagre. We have identified a novel secretory Leishmania donovani glycoprotein, Mevalonate kinase (MVK), and shown its importance in parasite internalization and immuno-modulation. In our studies, MVK was found to be secreted maximum after 1 h temperature stress at 37°C. Its secretion was increased by 6.5-fold in phagolysosome-like condition (pH ~5.5, 37°C) than at pH ~7.4 and 25°C. Treatment with MVK modulated host immune system by inducing interleukin-10 and interleukin-4 secretion, suppressing host’s ability to kill the parasite. Peripheral blood mononuclear cell (PBMC)-derived macrophages infected with mevalonate kinase-overexpressing parasites showed an increase in intracellular parasite burden in comparison to infection with vector control parasites. Mechanism behind the increase in phagocytosis and immunosuppression was found to be phosphorylation of mitogen-activated protein (MAP) kinase pathway protein, Extracellular signal-regulated kinases-1/2, and actin scaffold protein, cortactin. Thus, we conclude that Leishmania donovani Mevalonate kinase aids in parasite engulfment and subvert the immune system by interfering with signal transduction pathways in host cells, which causes suppression of the protective response and facilitates their persistence in the host. Our work elucidates the involvement of Leishmania in the process of phagocytosis which is thought to be dependent largely on macrophages and contributes towards better understanding of host pathogen interactions.

LPG2 Gene Duplication in Leishmania infantum: A Case for CRISPR-Cas9 Gene Editing

On the surface of the Leishmania promastigote, phosphoglycans (PG) such as lipophosphoglycan (LPG), proteophosphoglycan (PPG), free phosphoglycan polymers (PGs), and acid phosphatases (sAP), are dominant and contribute to the invasion and survival of Leishmania within the host cell by modulating macrophage signaling and intracellular trafficking. Phosphoglycan synthesis depends on the Golgi GDP-mannose transporter encoded by the LPG2 gene. Aiming to investigate the role of PG-containing molecules in Leishmania infantum infection process, herein we describe the generation and characterization of L. infantum LPG2-deficient parasites. This gene was unexpectedly identified as duplicated in the L. infantum genome, which impaired gene targeting using the conventional homologous recombination approach. This limitation was circumvented by the use of CRISPR/Cas9 technology. Knockout parasites were selected by agglutination assays using CA7AE antibodies followed by a lectin (RCA 120). Five clones were isolated and molecularly characterized, all revealing the expected edited genome, as well as the complete absence of LPG and PG-containing molecule expression. Finally, the deletion of LPG2 was found to impair the outcome of infection in human neutrophils, as demonstrated by a pronounced reduction (~83%) in intracellular load compared to wild-type parasite infection. The results obtained herein reinforce the importance of LPG and other PGs as virulence factors in host-parasite interactions.

Antileishmanial Effects of Synthetic EhPIb Analogs Derived from the Entamoeba histolytica Lipopeptidephosphoglycan

With an estimated number of new cases annually of approximately 1.4 million, leishmaniasis belongs to the most important parasitic diseases in the world. Nevertheless, existing drugs against leishmaniasis in general have several drawbacks that urgently necessitate new drug development. A glycolipid molecule of the intestinal protozoan parasite Entamoeba histolytica and its synthetic analogs previously showed considerable immunotherapeutic effects against Leishmania major infection.

With an estimated number of new cases annually of approximately 1.4 million, leishmaniasis belongs to the most important parasitic diseases in the world. Nevertheless, existing drugs against leishmaniasis in general have several drawbacks that urgently necessitate new drug development. A glycolipid molecule of the intestinal protozoan parasite Entamoeba histolytica and its synthetic analogs previously showed considerable immunotherapeutic effects against Leishmania major infection. Here, we designed and synthesized a series of new immunostimulatory compounds derived from the phosphatidylinositol b anchor of Entamoeba histolytica (EhPIb) subunit of the native compound and investigated their antileishmanial activity in vitro and in vivo in a murine model of cutaneous leishmaniasis. The new synthetic EhPIb analogs showed almost no toxicity in vitro. Treatment with the analogs significantly decreased the parasite load in murine and human macrophages in vitro. In addition, topical application of the EhPIb analog Eh-1 significantly reduced cutaneous lesions in the murine model, correlating with an increase in the production of selected Th1 cytokines. In addition, we could show in in vitro experiments that treatment with Eh-1 led to a decrease in mRNA expression of arginase-1 (Arg1) and interleukin 4 (IL-4), which are required by the parasites to circumvent their elimination by the immune response. The use of the host-targeting synthetic EhPIb compounds, either alone or in combination therapy with antiparasitic drugs, shows promise for treating cutaneous leishmaniasis and therefore might improve the current unsatisfactory status of chemotherapy against this infectious disease.

Leishmania donovani Lipophosphoglycan Increases Macrophage-Dependent Chemotaxis of CXCR6-Expressing Cells via CXCL16 Induction

CXCL16 is a multifunctional chemokine that is highly expressed by macrophages and other immune cells in response to bacterial and viral pathogens; however, little is known regarding the role of CXCL16 during parasitic infections. The protozoan parasite Leishmania donovani is the causative agent of visceral leishmaniasis. Even though chemokine production is a host defense mechanism during infection, subversion of the host chemokine system constitutes a survival strategy adopted by the parasite. Here, we report that L. donovani promastigotes upregulate CXCL16 synthesis and secretion by bone marrow-derived macrophages (BMDM). In contrast to wild-type parasites, a strain deficient in the virulence factor lipophosphoglycan (LPG) failed to induce CXCL16 production. Consistent with this, cell treatment with purified L. donovani LPG augmented CXCL16 expression and secretion. Notably, the ability of BMDM to promote migration of cells expressing CXCR6, the cognate receptor of CXCL16, was augmented upon L. donovani infection in a CXCL16- and LPG-dependent manner. Mechanistically, CXCL16 induction by L. donovani required the activity of AKT and the mechanistic target of rapamycin (mTOR) but was independent of Toll-like receptor signaling. Collectively, these data provide evidence that CXCL16 is part of the inflammatory response elicited by L. donovani LPG in vitro Further investigation using CXCL16 knockout mice is required to determine whether this chemokine contributes to the pathogenesis of visceral leishmaniasis and to elucidate the underlying molecular mechanisms.

Potential of Pluronics® P-123 and F-127 as nanocarriers of anti-Leishmania chemotherapy

Leishmaniasis is a neglected disease and drugs approved for its treatment often lead to abandonment, failure of therapy and even death. Photodynamic therapy (PDT) has been shown to be a promising, non-invasive and selective for a target region without requiring high-cost technology. Usually, it is employed a photosensitizing agent (PS) incorporated into nanoparticles (NP). Pluronics^® P-123 and F-127 micelles are very interesting aqueous NP promoting efficient and selective delivery and less adverse effects. This study aimed to detect the activity of Pluronics^® P-123 and F-127 themselves since there is a scarcity of data on these NP activities without drugs incorporation. This study evaluated, in vitro, the activity of Pluronics^® against promastigotes and amastigotes of Leishmania amazonensis and also their cytotoxicities. Additionally, the determination of the mitochondria membrane potential in promastigotes, internalization of these Pluronics^® in the parasite membrane and macrophages and its stability in the culture medium was evaluated. Results showed that Pluronics^® did not cause significant damage to human red cells and promastigotes. The P-123 and F-127 inhibited the survival rate of L. amazonensis amastigotes, and also presented loss of mitochondrial membrane potential on promastigotes. The Pluronics^® showed low cytotoxic activity on J774A.1 macrophages, while only P-123 showed moderate cytotoxicity for BALB/c macrophages. The stability of P-123 and F-127 in culture medium was maintained for ten days. In conclusion, the NP studied can be used for incorporating potent leishmanicidal chemotherapy, due to their selectivity towards macrophages, being a promising system for the treatment of cutaneous leishmaniasis.

An overview on Leishmania (Mundinia) enriettii: biology, immunopathology, LRV and extracellular vesicles during the host-parasite interaction

One of the Leishmania species known to be non-infective to humans is Leishmania (Mundinia) enriettii whose vertebrate host is the guinea pig Cavia porcellus. It is a good model for cutaneous leishmaniasis, chemotherapeutic and molecular studies. In the last years, an increased interest has emerged concerning the L. (Mundinia) subgenus after the finding of Leishmania (M.) macropodum in Australia and with the description of other new/putative species such as L. (M.) martiniquensis and 'L. (M.) siamensis'. This review focused on histopathology, glycoconjugates and innate immunity. The presence of Leishmania RNA virus and shedding of extracellular vesicles by the parasite were also evaluated.

Leishmania enriettii: biochemical characterisation of lipophosphoglycans (LPGs) and glycoinositolphospholipids (GIPLs) and infectivity to Cavia porcellus

BACKGROUND

Leishmania enriettii is a species non-infectious to man, whose reservoir is the guinea pig Cavia porcellus. Many aspects of the parasite-host interaction in this model are unknown, especially those involving parasite surface molecules. While lipophosphoglycans (LPGs) and glycoinositolphospholipids (GIPLs) of Leishmania species from the Old and New World have already been described, glycoconjugates of L. enriettii and their importance are still unknown.

METHODS

Mice peritoneal macrophages from C57BL/6 and knock-out (TLR2 -/-, TLR4 -/-) were primed with IFN-γ and stimulated with purified LPG and GIPLs from both species. Nitric oxide and cytokine production were performed. MAPKs (p38 and JNK) and NF-kB activation were evaluated in J774.1 macrophages and CHO cells, respectively.

RESULTS

LPGs were extracted, purified and analysed by western-blot, showing that LPG from L88 strain was longer than that of Cobaia strain. LPGs and GIPLs were depolymerised and their sugar content was determined. LPGs from both strains did not present side chains, having the common disaccharide Gal(β1,4)Man(α1)-PO4. The GIPL from L88 strain presented galactose in its structure, suggestive of type II GIPL. On the other hand, the GIPL of Cobaia strain presented an abundance of glucose, a characteristic not previously observed. Mice peritoneal macrophages from C57BL/6 and knock-outs (TLR2 -/- and TLR4 -/-) were primed with IFN-γ and stimulated with glycoconjugates and live parasites. No activation of NO or cytokines was observed with live parasites. On the other hand, LPGs and GIPLs were able to activate the production of NO, IL-6, IL-12 and TNF-α preferably via TRL2. However, in CHO cells, only GIPLs were able to activate TRL2 and TRL4. In vivo studies using male guinea pigs (Cavia porcellus) showed that only strain L88 was able to develop more severe ulcerated lesions especially in the presence of salivary gland extract (SGE).

CONCLUSION

The two L. enriettii strains exhibited polymorphisms in their LPGs and GIPLs and those features may be related to a more pro-inflammatory profile in the L88 strain.

Leishmania major inhibits IL-12 in macrophages by signalling through CR3 (CD11b/CD18) and down-regulation of ETS-mediated transcription

Leishmania major is an aetiological agent of cutaneous leishmaniasis. The parasite primarily infects immune sentinel cells, specifically macrophages and dendritic cells, in the mammalian host. Infection is receptor mediated and is known to involve parasite binding to cell surface protein complement receptor 3 (CR3, Mac-1, CD11b/CD18). Engagement of CR3 by various ligands inhibits production of interleukin-12 (IL-12), the cytokine that drives antileishmanial T helper 1-type immune responses. Likewise, L. major infection inhibits IL-12 production and activation of host macrophages. Our data indicate that in the absence of CR3, L. major-infected bone marrow-derived macrophages produce more IL-12 and nitric oxide compared with WT cells upon lipopolysaccharide (LPS) stimulation. We therefore investigated multiple signalling pathways by which L. major may inhibit IL-12 transcription through CR3 ligation. We demonstrate that L. major infection does not elicit significant NFκB p65, MAPK, IRF-1 or IRF-8 activation in WT or CD11b-deficient macrophages. Furthermore, infection neither inhibits LPS-induced MAPK or NFκB activation nor blocks IFN-γ-activated IRF-1 and IRF-8. ETS-mediated transcription, however, is inhibited by L. major infection independently of CR3. Our data indicate that L. major-mediated inhibition of IL-12 occurs through CR3 engagement; however, the mechanism of inhibition is independent of NFκB, MAPK, IRF and ETS.

Leishmania mexicana lipophosphoglycan activates ERK and p38 MAP kinase and induces production of proinflammatory cytokines in human macrophages through TLR2 and TLR4

Protozoan parasites of genus Leishmania are the causative agents of leishmaniasis. Leishmania promastigotes primarily infect macrophages in the host, where they transform into amastigotes and multiply. Lipophosphoglycan (LPG), the most abundant surface molecule of the parasite, is a virulence determinant that regulates the host immune response. Promastigotes are able to modulate this effect through LPG, creating a favourable environment for parasite survival, although the mechanisms underlying this modulation remain unknown. We analysed the participation of TLR2 and TLR4 in the production of cytokines and explored the possible phosphorylation of ERK and/or p38 MAP kinase signalling cascades in human macrophages stimulated with Leishmania mexicana LPG. The results show that LPG induced the production of TNF-α, IL-1β, IL-12p40, IL-12p70 and IL-10 and led to phosphorylation of ERK and p38 MAP kinase. Specific inhibitors of ERK or p38 MAP kinases and mAbs against TLR2 and TLR4 reduced cytokine production and phosphorylation of both kinases. Our results suggest that L. mexicana LPG binds TLR2 and TLR4 receptors in human macrophages, leading to ERK and MAP kinase phosphorylation and production of pro-inflammatory cytokines.

The early interaction of Leishmania with macrophages and dendritic cells and its influence on the host immune response

The complicated interactions between Leishmania and the host antigen-presenting cells (APCs) have fundamental effects on the final outcome of the disease. Two major APCs, macrophages and dendritic cells (DCs), play critical roles in mediating resistance and susceptibility during Leishmania infection. Macrophages are the primary resident cell for Leishmania: they phagocytose and permit parasite proliferation. However, these cells are also the major effector cells to eliminate infection. The effective clearance of parasites by macrophages depends on activation of appropriate immune response, which is usually initiated by DCs. Here, we review the early interaction of APCs with Leishmania parasites and how these interactions profoundly impact on the ensuing adaptive immune response. We also discuss how the current knowledge will allow further refinement of our understanding of the interplay between Leishmania and its hosts that leads to resistance or susceptibility.

Leishmania donovani exploits host deubiquitinating enzyme A20, a negative regulator of TLR signaling, to subvert host immune response

TLRs, which form an interface between mammalian host and microbe, play a key role in pathogen recognition and initiation of proinflammatory response thus stimulating antimicrobial activity and host survival. However, certain intracellular pathogens such as Leishmania can successfully manipulate the TLR signaling, thus hijacking the defensive strategies of the host. Despite the presence of lipophosphoglycan, a TLR2 ligand capable of eliciting host-defensive cytokine response, on the surface of Leishmania, the strategies adopted by the parasite to silence the TLR2-mediated proinflammatory response is not understood. In this study, we showed that Leishmania donovani modulates the TLR2-mediated pathway in macrophages through inhibition of the IKK-NF-κB cascade and suppression of IL-12 and TNF-α production. This may be due to impairment of the association of TRAF6 with the TAK-TAB complex, thus inhibiting the recruitment of TRAF6 in TLR2 signaling. L. donovani infection drastically reduced Lys 63-linked ubiquitination of TRAF6, and the deubiquitinating enzyme A20 was found to be significantly upregulated in infected macrophages. Small interfering RNA-mediated silencing of A20 restored the Lys 63-linked ubiquitination of TRAF6 as well as IL-12 and TNF-α levels with a concomitant decrease in IL-10 and TGF-β synthesis in infected macrophages. Knockdown of A20 led to lower parasite survival within macrophages. Moreover, in vivo silencing of A20 by short hairpin RNA in BALB/c mice led to increased NF-κB DNA binding and host-protective proinflammatory cytokine response resulting in effective parasite clearance. These results suggest that L. donovani might exploit host A20 to inhibit the TLR2-mediated proinflammatory gene expression, thus escaping the immune responses of the host.

Infection of neutrophil granulocytes with Leishmania major activates ERK 1/2 and modulates multiple apoptotic pathways to inhibit apoptosis

Neutrophil granulocytes provide the first line of defense against bacterial, fungal, and parasitic infections. They phagocytose and kill many invading pathogens. Certain pathogenic microorganisms such as the intracellular protozoan parasite Leishmania major (L. major) can survive inside neutrophils. Mature neutrophils have a very short life span due to spontaneous apoptosis. Previously, we have reported that infections with L. major are able to delay spontaneous apoptosis. In the present study, we addressed the underlying mechanisms of regulation of both extrinsic and intrinsic apoptosis. We show that interaction with L. major transiently activates ERK1/2 phosphorylation. Pharmacological inhibition of ERK1/2 phosphorylation reversed the apoptosis delay. Moreover, infection leads to the enhanced and sustainable expression of the anti-apoptotic proteins Bcl-2 and Bfl-1, respectively. As downstream events, the release of cytochrome c from mitochondria and processing of caspase-6 were inhibited. We also confirm that infection with L. major results in reduced FAS expression on the surface of neutrophils. The presented data indicate that infection with L. major affects both intrinsic as well as extrinsic pathways of neutrophil apoptosis. Enhanced life span of host neutrophils enables the parasite to survive within neutrophils.

Secreted virulence factors and immune evasion in visceral leishmaniasis

Evasion or subversion of host immune responses is a well-established paradigm in infection with visceralizing leishmania. In this review, we summarize current findings supporting a model in which leishmania target host regulatory molecules and pathways, such as the PTP SHP-1 and the PI3K/Akt signaling cascade, to prevent effective macrophage activation. Furthermore, we describe how virulence factors, secreted by leishmania, interfere with macrophage intracellular signaling. Finally, we discuss mechanisms of secretion and provide evidence that leishmania use a remarkably adept, exosome-based secretion mechanism to export and deliver effector molecules to host cells. In addition to representing a novel mechanism for trafficking of virulence factors across membranes, recent findings indicate that leishmania exosomes may have potential as vaccine candidates.

Glycoconjugates in New World species of Leishmania: polymorphisms in lipophosphoglycan and glycoinositolphospholipids and interaction with hosts

BACKGROUND

Protozoan parasites of the genus Leishmania cause a number of important diseases in humans and undergo a complex life cycle, alternating between a sand fly vector and vertebrate hosts. The parasites have a remarkable capacity to avoid destruction in which surface molecules are determinant for survival. Amongst the many surface molecules of Leishmania, the glycoconjugates are known to play a central role in host-parasite interactions and are the focus of this review.

SCOPE OF THE REVIEW

The most abundant and best studied glycoconjugates are the Lipophosphoglycans (LPGs) and glycoinositolphospholipids (GIPLs). This review summarizes the main studies on structure and biological functions of these molecules in New World Leishmania species.

MAJOR CONCLUSIONS

LPG and GIPLs are complex molecules that display inter- and intraspecies polymorphisms. They are key elements for survival inside the vector and to modulate the vertebrate immune response during infection.

GENERAL SIGNIFICANCE

Most of the studies on glycoconjugates focused on Old World Leishmania species. Here, it is reported some of the studies involving New World species and their biological significance on host-parasite interaction. This article is part of a Special Issue entitled Glycoproteomics.

Leishmania mexicana promastigotes inhibit macrophage IL-12 production via TLR-4 dependent COX-2, iNOS and arginase-1 expression

The effects of Leishmania mexicana metacyclic promastigotes upon MAP kinase signalling in mouse bone marrow macrophages and subsequent expression of the disease regulatory proteins iNOS and COX-2 were studied. At a ratio of 5:1, promastigotes caused a marked increase in phosphorylation of the three major MAP kinases, ERK, p38 and JNK. MAP kinase signalling was substantially reduced in TLR-4^−/− but not TLR-2^−/− deficient macrophages and completely abolished in double TLR-2/4^−/− macrophages. A similar outcome was observed using cysteine peptidase B deficient amastigotes. Furthermore, whilst promastigotes had no independent effect on iNOS or COX-2 expression, they prolonged the induction of these proteins stimulated by LPS and enhanced PGE₂ and NO production. Induction of COX-2 and iNOS was also TLR-4 dependent. Blockade of either PGE₂ or NO production with indomethacin or l-NAME reversed promastigote inhibition of LPS induced IL-12 production. Promastigotes also increased macrophage arginase-1 expression and enhanced arginase activity, both of which were substantially reduced in TLR-4 but not TLR-2 deficient macrophages. Surprisingly, arginase inhibition by Nor-NOHA also caused a reversal of promastigote mediated inhibition of macrophage IL-12 production. These data demonstrate for the first time the role of TLR-4 in mediating the effects of L. mexicana promastigotes on MAP kinase activation, up-regulation of COX-2, iNOS as well as arginase-1 expression in macrophages and further shows that PGE₂, NO and arginase activity all contribute substantially to the inhibition of host cell IL-12 production.

Evasion of Host Defence by Leishmania donovani: Subversion of Signaling Pathways

Protozoan parasites of the genus Leishmania are responsible for causing a variety of human diseases known as leishmaniasis, which range from self-healing skin lesions to severe infection of visceral organs that are often fatal if left untreated. Leishmania donovani (L. donovani), the causative agent of visceral leishmaniasis, exemplifys a devious organism that has developed the ability to invade and replicate within host macrophage. In fact, the parasite has evolved strategies to interfere with a broad range of signaling processes in macrophage that includes Protein Kinase C, the JAK2/STAT1 cascade, and the MAP Kinase pathway. This paper focuses on how L. donovani modulates these signaling pathways that favour its survival and persistence in host cells.

Leishmania interferes with host cell signaling to devise a survival strategy

The protozoan parasite Leishmania spp. exists as extracellular promastigotes in its vector whereas it resides and replicates as amastigotes within the macrophages of its mammalian host. As a survival strategy, Leishmania modulates macrophage functions directly or indirectly. The direct interference includes prevention of oxidative burst and the effector functions that lead to its elimination. The indirect effects include the antigen presentation and modulation of T cell functions in such a way that the effector T cells help the parasite survive by macrophage deactivation. Most of these direct and indirect effects are regulated by host cell receptor signaling that occurs through cycles of phosphorylation and dephosphorylation in cascades of kinases and phosphatases. This review highlights how Leishmania selectively manipulates the different signaling pathways to ensure its survival.

The Leishmania surface protease GP63 cleaves multiple intracellular proteins and actively participates in p38 mitogen-activated protein kinase inactivation

The Leishmania parasite is a widespread disease threat in tropical areas, causing symptoms ranging from skin lesions to death. Leishmania parasites typically invade macrophages but are also capable of infecting fibroblasts, which may serve as a reservoir for recurrent infection. Invasion by intracellular pathogens often involves exploitation of the host cell cytoskeletal and signaling machinery. Here we have observed a dramatic rearrangement of the actin cytoskeleton and marked modifications in the profile of protein tyrosine phosphorylation in fibroblasts infected with Leishmania major. Correspondingly, exposure to L. major resulted in degradation of the phosphorylated adaptor protein p130Cas and the protein-tyrosine phosphatase-PEST. Cellular and in vitro assays using pharmacological protease inhibitors, recombinant enzyme, and genetically modified strains of L. major identified the parasite protease GP63 as the principal catalyst of proteolysis during infection. A number of additional signaling proteins were screened for degradation during L. major infection as follows: a small subset was cleaved, including cortactin, T-cell protein-tyrosine phosphatase, and caspase-3, but the majority remained unaffected. Protein degradation occurred in cells incubated with Leishmania extracts in the absence of intact parasites, suggesting a mechanism permitting transfer of functional GP63 into the intracellular space. Finally, we evaluated the impact of Leishmania on MAPK signaling; unlike p44/42 and JNK, p38 was inactivated upon infection in a GP63- and protein degradation-dependent manner, which likely involves cleavage of the upstream adaptor TAB1. Our results establish that GP63 plays a central role in a number of hostcell molecular events that likely contribute to the infectivity of Leishmania.

Leishmania promastigotes activate PI3K/Akt signalling to confer host cell resistance to apoptosis

Previous reports have shown that cells infected with promastigotes of some Leishmania species are resistant to the induction of apoptosis. This would suggest that either parasites elaborate factors that block signalling from apoptosis inducers or that parasites engage endogenous host signalling pathways that block apoptosis. To investigate the latter scenario, we determined whether Leishmania infection results in the activation of signalling pathways that have been shown to mediate resistance to apoptosis in other infection models. First, we showed that infection with the promastigote form of Leishmania major, Leishmania pifanoi and Leishmania amazonensis activates signalling through p38 mitogen-activated protein kinase (MAPK), NFkappaB and PI3K/Akt. Then we found that inhibition of signalling through the PI3K/Akt pathway with LY294002 and Akt IV inhibitor reversed resistance of infected bone marrow-derived macrophages and RAW 264.7 macrophages to potent inducers of apoptosis. Moreover, reduction of Akt levels with small interfering RNAs to Akt resulted in the inability of infected macrophages to resist apoptosis. Further evidence of the role of PI3K/Akt signalling in the promotion of cell survival by infected cells was obtained with the finding that Bad, which is a substrate of Akt, becomes phosphorylated during the course of infection. In contrast to the observations with PI3K/Akt signalling, inhibition of p38 MAPK signalling with SB202190 or NFkappaB signalling with wedelolactone had limited effect on parasite-induced resistance to apoptosis. We conclude that Leishmania promastigotes engage PI3K/Akt signalling, which confers to the infected cell, the capacity to resist death from activators of apoptosis.

Leishmania major: Reactive oxygen species and interferon gamma induction by soluble lipophosphoglycan of stationary phase promastigotes

Protozoan parasites of the genus Leishmania cause a number of important human diseases. One of the key determinants of parasite infectivity and survival is membrane glycoconjugate lipophosphoglycan (mLPG). In addition, it has been shown that mLPG could be used as a transmission blocking vaccine. Since culture supernatant of parasite promastigotes is a good source of LPG, we attempted to compare the immunological properties of culture supernatant and membrane LPG prepared from stationary phase promastigotes of Leishmania major. The purity of supernatant LPG (sLPG) and membrane LPG (mLPG) was determined by thin layer chromatography. The effect of sLPG and mLPG on the production of reactive oxygen species (ROS) was studied using PBMCs isolated from healthy individuals. In addition, induction of IL-12, IFN-gamma and IL-10 secretion in the presence of sLPG and mLPG was investigated. Reactive oxygen species in addition to IL-10 and IL-12 were induced by both sLPG and mLPG. However, IFN-gamma production was promoted only in response to sLPG suggesting its ability to promote Th1 response and implication in vaccine design.

Protein kinases as targets for antimalarial intervention: Kinomics, structure-based design, transmission-blockade, and targeting host cell enzymes

The surge of interest in protein kinases as targets for chemotherapeutic intervention in a number of diseases such as cancer and neurodegenerative disorders has stimulated research aimed at determining whether enzymes of this class might also be considered as targets in the context of diseases caused by parasitic protists. Here, we present an overview of recent developments in this field, concentrating (i) on the benefits gained from the availability of genomic databases for a number of parasitic protozoa, (ii) on the emerging field of structure-aided design of inhibitors targeting protein kinases of parasitic protists, (iii) on the concept known as transmission-blockade, whereby kinases implicated in the development of the parasite in their arthropod vector might be targeted to interfere with disease transmission, and (iv) on the possibility of controlling parasitic diseases through the inhibition of host cell protein kinases that are required for the establishment of infection by the parasites.