Leishmania infection inhibits macrophage motility by altering F-actin dynamics and the expression of adhesion complex proteins

Hypermigration of macrophages through the concerted action of GRA effectors on NF-κB/p38 signaling and host chromatin accessibility potentiates Toxoplasma dissemination

Mononuclear phagocytes facilitate the dissemination of the obligate intracellular parasite Toxoplasma gondii. Here, we report how a set of secreted parasite effector proteins from dense granule organelles (GRA) orchestrates dendritic cell-like chemotactic and pro-inflammatory activation of parasitized macrophages. These effects enabled efficient dissemination of the type II T. gondii lineage, a highly prevalent genotype in humans. We identify novel functions for effectors GRA15 and GRA24 in promoting CCR7-mediated macrophage chemotaxis by acting on NF-κB and p38 mitogen-activated protein kinase signaling pathways, respectively, with contributions by GRA16/18 and counter-regulation by effector TEEGR. Furthermore, GRA28 boosted chromatin accessibility and GRA15/24/NF-κB-dependent transcription at the Ccr7 gene locus in primary macrophages. In vivo, adoptively transferred macrophages infected with wild-type T. gondii outcompeted macrophages infected with a GRA15/24 double mutant in migrating to secondary organs in mice. The data show that T. gondii, rather than being passively shuttled, actively promotes its dissemination by inducing a finely regulated pro-migratory state in parasitized human and murine phagocytes via co-operating polymorphic GRA effectors.

IMPORTANCE

Intracellular pathogens can hijack the cellular functions of infected host cells to their advantage, for example, for intracellular survival and dissemination. However, how microbes orchestrate the hijacking of complex cellular processes, such as host cell migration, remains poorly understood. As such, the common parasite Toxoplasma gondii actively invades the immune cells of humans and other vertebrates and modifies their migratory properties. Here, we show that the concerted action of a number of secreted effector proteins from the parasite, principally GRA15 and GRA24, acts on host cell signaling pathways to activate chemotaxis. Furthermore, the protein effector GRA28 selectively acted on chromatin accessibility in the host cell nucleus to selectively boost host gene expression. The joint activities of GRA effectors culminated in pro-migratory signaling within the infected phagocyte. We provide a molecular framework delineating how T. gondii can orchestrate a complex biological phenotype, such as the migratory activation of phagocytes to boost dissemination.

Leishmania donovani mevalonate kinase regulates host actin for inducing phagocytosis

Despite the well-established role of macrophages in phagocytosing Leishmania, the contribution of the parasite to this process is not well understood. Present study provides insights into the mechanism underlying the MVK-induced entry of L. donovani and improve our knowledge of host-pathogen interactions. We have discussed Mevalonate kinase (MVK)-induced actin reorganization, modulation of signaling pathways and host cell functions. Our results show that LdMVK gains access to macrophage cytosol and induces actin assembly modulation through the activation of actin-related proteins: VASP, Src and ERM. We have also demonstrated that LdMVK induces Ca2+ signaling and Akt pathway in macrophages, which are critical components of Leishmania survival and proliferation. Interestingly, we found that antibodies against LdMVK can kill Leishmania-infected macrophages in culture by forming extracellular traps, highlighting the potential of LdMVK in inhibiting parasite death. Overall, LdMVK is a virulent factor in Leishmania that mediates parasite internalization and host modulation by targeting host proteins phosphorylation and calcium homeostasis having significant implications in disease progression.

Hypermigration of macrophages through the concerted action of GRA effectors on NF-κB/p38 signaling and host chromatin accessibility potentiates Toxoplasma dissemination

Mononuclear phagocytes facilitate the dissemination of the obligate intracellular parasite Toxoplasma gondii. Here, we report how a set of secreted parasite effector proteins from dense granule organelles (GRA) orchestrates dendritic cell-like chemotactic and pro-inflammatory activation of parasitized macrophages. These effects enabled efficient dissemination of the type II T. gondii lineage, a highly prevalent genotype in humans. We identify novel functions for effectors GRA15 and GRA24 in promoting CCR7-mediated macrophage chemotaxis by acting on NF-κB and p38 MAPK signaling pathways, respectively, with contributions of GRA16/18 and counter-regulation by effector TEEGR. Further, GRA28 boosted chromatin accessibility and GRA15/24/NF-κB-dependent transcription at the Ccr7 gene locus in primary macrophages. In vivo, adoptively transferred macrophages infected with wild-type T. gondii outcompeted macrophages infected with a GRA15/24 double mutant in migrating to secondary organs in mice. The data show that T. gondii, rather than being passively shuttled, actively promotes its dissemination by inducing a finely regulated pro-migratory state in parasitized human and murine phagocytes via co-operating polymorphic GRA effectors.

Leishmania infection alters macrophage and dendritic cell migration in a three-dimensional environment

Background: Leishmaniasis results in a wide spectrum of clinical manifestations, ranging from skin lesions at the site of infection to disseminated lesions in internal organs, such as the spleen and liver. While the ability of Leishmania-infected host cells to migrate may be important to lesion distribution and parasite dissemination, the underlying mechanisms and the accompanying role of host cells remain poorly understood. Previously published work has shown that Leishmania infection inhibits macrophage migration in a 2-dimensional (2D) environment by altering actin dynamics and impairing the expression of proteins involved in plasma membrane-extracellular matrix interactions. Although it was shown that L. infantum induces the 2D migration of dendritic cells, in vivo cell migration primarily occurs in 3-dimensional (3D) environments. The present study aimed to investigate the migration of macrophages and dendritic cells infected by Leishmania using a 3-dimensional environment, as well as shed light on the mechanisms involved in this process. Methods: Following the infection of murine bone marrow-derived macrophages (BMDM), human macrophages and human dendritic cells by L. amazonensis, L. braziliensis, or L. infantum, cellular migration, the formation of adhesion complexes and actin polymerization were evaluated. Results: Our results indicate that Leishmania infection inhibited 3D migration in both BMDM and human macrophages. Reduced expression of proteins involved in adhesion complex formation and alterations in actin dynamics were also observed in Leishmania-infected macrophages. By contrast, increased human dendritic cell migration in a 3D environment was found to be associated with enhanced adhesion complex formation and increased actin dynamics. Conclusion: Taken together, our results show that Leishmania infection inhibits macrophage 3D migration, while enhancing dendritic 3D migration by altering actin dynamics and the expression of proteins involved in plasma membrane extracellular matrix interactions, suggesting a potential association between dendritic cells and disease visceralization.

The Toxoplasma effector GRA28 promotes parasite dissemination by inducing dendritic cell-like migratory properties in infected macrophages

Upon pathogen detection, macrophages normally stay sessile in tissues while dendritic cells (DCs) migrate to secondary lymphoid tissues. The obligate intracellular protozoan Toxoplasma gondii exploits the trafficking of mononuclear phagocytes for dissemination via unclear mechanisms. We report that, upon T. gondii infection, macrophages initiate the expression of transcription factors normally attributed to DCs, upregulate CCR7 expression with a chemotactic response, and perform systemic migration when adoptively transferred into mice. We show that parasite effector GRA28, released by the MYR1 secretory pathway, cooperates with host chromatin remodelers in the host cell nucleus to drive the chemotactic migration of parasitized macrophages. During in vivo challenge studies, bone marrow-derived macrophages infected with wild-type T. gondii outcompeted those challenged with MYR1- or GRA28-deficient strains in migrating and reaching secondary organs. This work reveals how an intracellular parasite hijacks chemotaxis in phagocytes and highlights a remarkable migratory plasticity in differentiated cells of the mononuclear phagocyte system.

Identification of the Host Substratome of Leishmania-Secreted Casein Kinase 1 Using a SILAC-Based Quantitative Mass Spectrometry Assay

Leishmaniasis is a severe public health problem, caused by the protozoan Leishmania. This parasite has two developmental forms, extracellular promastigote in the insect vector and intracellular amastigote in the mammalian host where it resides inside the phagolysosome of macrophages. Little is known about the virulence factors that regulate host-pathogen interactions and particularly host signalling subversion. All the proteomes of Leishmania extracellular vesicles identified the presence of Leishmania casein kinase 1 (L-CK1.2), a signalling kinase. L-CK1.2 is essential for parasite survival and thus might be essential for host subversion. To get insights into the functions of L-CK1.2 in the macrophage, the systematic identification of its host substrates is crucial, we thus developed an easy method to identify substrates, combining phosphatase treatment, in vitro kinase assay and Stable Isotope Labelling with Amino acids in Cell (SILAC) culture-based mass spectrometry. Implementing this approach, we identified 225 host substrates as well as a potential novel phosphorylation motif for CK1. We confirmed experimentally the enrichment of our substratome in bona fide L-CK1.2 substrates and showed they were also phosphorylated by human CK1δ. L-CK1.2 substratome is enriched in biological processes such as "viral and symbiotic interaction," "actin cytoskeleton organisation" and "apoptosis," which are consistent with the host pathways modified by Leishmania upon infection, suggesting that L-CK1.2 might be the missing link. Overall, our results generate important mechanistic insights into the signalling of host subversion by these parasites and other microbial pathogens adapted for intracellular survival.

Leishmania-Induced Dendritic Cell Migration and Its Potential Contribution to Parasite Dissemination

Leishmania, an intracellular parasite species, causes lesions on the skin and in the mucosa and internal organs. The dissemination of infected host cells containing Leishmania is crucial to parasite survival and the establishment of infection. Migratory phenomena and the mechanisms underlying the dissemination of Leishmania-infected human dendritic cells (hDCs) remain poorly understood. The present study aimed to investigate differences among factors involved in hDC migration by comparing infection with visceral leishmaniasis (VL) induced by Leishmaniainfantum with diverse clinical forms of tegumentary leishmaniasis (TL) induced by Leishmaniabraziliensis or Leishmania amazonensis. Following the infection of hDCs by isolates obtained from patients with different clinical forms of Leishmania, the formation of adhesion complexes, actin polymerization, and CCR7 expression were evaluated. We observed increased hDC migration following infection with isolates of L. infantum (VL), as well as disseminated (DL) and diffuse (DCL) forms of cutaneous leishmaniasis (CL) caused by L. braziliensis and L. amazonensis, respectively. Increased expression of proteins involved in adhesion complex formation and actin polymerization, as well as higher CCR7 expression, were seen in hDCs infected with L. infantum, DL and DCL isolates. Together, our results suggest that hDCs play an important role in the dissemination of Leishmania parasites in the vertebrate host.

Complement receptor 3 mediates ruffle-like, actin-rich aggregates during phagocytosis of Leishmania infantum metacyclics

The parasitic protozoan Leishmania infantum resides primarily in macrophages throughout mammalian infection. Infection is initiated by deposition of the metacyclic promastigote into the dermis of a mammalian host by the sand fly vector. Promastigotes enter macrophages by ligating surface receptors such as complement receptor 3 (CR3), inducing phagocytosis of the parasite. At the binding site of metacyclic promastigotes, we observed large asymmetrical aggregates of macrophage membrane with underlying actin, resembling membrane ruffles. Actin accumulation was observed at the point of initial contact, before phagosome formation and accumulation of peri-phagosomal actin. Ruffle-like structures did not form during phagocytosis of attenuated promastigotes or during phagocytosis of the intracellular amastigote form of L. infantum. Entry of promastigotes through massive actin accumulation was associated with a subsequent delay in fusion of the parasitophorous vacuole (PV) with the lysosomal markers LAMP-1 and Cathepsin D. Actin accumulation was also associated with entry through CR3, since macrophages from CD11b knockout (KO) mice did not form massive aggregates of actin during phagocytosis of metacyclic promastigotes. Furthermore, intracellular survival of L. infantum was significantly decreased in CD11b KO compared to wild type macrophages, although entry rates were similar. We conclude that both promastigote virulence and host cell CR3 are needed for the formation of ruffle-like membrane structures at the site of metacyclic promastigote phagocytosis, and that formation of actin-rich aggregates during entry correlates with the intracellular survival of virulent promastigotes.

Leishmania infantum Enhances Migration of Macrophages via a Phosphoinositide 3-Kinase γ-Dependent Pathway

Leishmania infantum (L. infantum) and Leishmania major (L. major) are phylogenetically related protozoan parasites that cause different pathologies in humans (visceral and cutaneous infections, respectively). Here, we report on how these obligatory intracellular pathogens differentially affect the migration of macrophages. Resorting to gap closure assays of infected murine bone marrow derived macrophages, we observed that L. infantum enhances the mobility of these cells. This is not the case of L. major, whose impact on macrophage migration is null. Resorting to kinase inhibition assays, we witnessed that chemical inhibition of phosphoinositide 3-kinase-γ (PI3Kγ) critically impairs cell mobility in all experimental conditions. Importantly, the blockade of tyrosine kinases with dasatinib also slows down naı̈ve and L. major-parasitized cells but not macrophages exposed to L. infantum. The dasatinib-resistant phenotype of L. infantum-infected macrophages aligns with the hypothesis that this parasite invokes a tyrosine kinase-independent pathway to increase the PI3Kγ activity of macrophages and enhance migration.

Anti-Leishmanial Vaccines: Assumptions, Approaches, and Annulments

Leishmaniasis is a neglected protozoan parasitic disease that occurs in 88 countries but a vaccine is unavailable. Vaccination with live, killed, attenuated (physically or genetically) Leishmania have met with limited success, while peptide-, protein-, or DNA-based vaccines showed promise only in animal models. Here, we critically assess several technical issues in vaccination and expectation of a host-protective immune response. Several studies showed that antigen presentation during priming and triggering of the same cells in infected condition are not comparable. Altered proteolytic processing, antigen presentation, protease-susceptible sites, and intracellular expression of pathogenic proteins during Leishmania infection may vary dominant epitope selection, MHC-II/peptide affinity, and may deter the reactivation of desired antigen-specific T cells generated during priming. The robustness of the memory T cells and their functions remains a concern. Presentation of the antigens by Leishmania-infected macrophages to antigen-specific memory T cells may lead to change in the T cells' functional phenotype or anergy or apoptosis. Although cells may be activated, the peptides generated during infection may be different and cross-reactive to the priming peptides. Such altered peptide ligands may lead to suppression of otherwise active antigen-specific T cells. We critically assess these different immunological issues that led to the non-availability of a vaccine for human use.

Trypanosoma cruzi down-regulates mechanosensitive proteins in cardiomyocytes

BACKGROUND

Cardiac physiology depends on coupling and electrical and mechanical coordination through the intercalated disc. Focal adhesions offer mechanical support and signal transduction events during heart contraction-relaxation processes. Talin links integrins to the actin cytoskeleton and serves as a scaffold for the recruitment of other proteins, such as paxillin in focal adhesion formation and regulation. Chagasic cardiomyopathy is caused by infection by Trypanosoma cruzi and is a debilitating condition comprising extensive fibrosis, inflammation, cardiac hypertrophy and electrical alterations that culminate in heart failure.

OBJECTIVES

Since mechanotransduction coordinates heart function, we evaluated the underlying mechanism implicated in the mechanical changes, focusing especially in mechanosensitive proteins and related signalling pathways during infection of cardiac cells by T. cruzi.

METHODS

We investigated the effect of T. cruzi infection on the expression and distribution of talin/paxillin and associated proteins in mouse cardiomyocytes in vitro by western blotting, immunofluorescence and quantitative real-time polymerase chain reaction (qRT-PCR).

FINDINGS

Talin and paxillin spatial distribution in T. cruzi-infected cardiomyocytes in vitro were altered associated with a downregulation of these proteins and mRNAs levels at 72 h post-infection (hpi). Additionally, we observed an increase in the activation of the focal adhesion kinase (FAK) concomitant with increase in β-1-integrin at 24 hpi. Finally, we detected a decrease in the activation of FAK at 72 hpi in T. cruzi-infected cultures.

MAIN CONCLUSION

The results suggest that these changes may contribute to the mechanotransduction disturbance evidenced in chagasic cardiomyopathy.

CD100/Sema4D Increases Macrophage Infection by Leishmania (Leishmania) amazonensis in a CD72 Dependent Manner

Leishmaniasis is caused by trypanosomatid protozoa of the genus Leishmania, which infect preferentially macrophages. The disease affects 12 million people worldwide, who may present cutaneous, mucocutaneous or visceral forms. Several factors influence the form and severity of the disease, and the main ones are the Leishmania species and the host immune response. CD100 is a membrane bound protein that can also be shed. It was first identified in T lymphocytes and latter shown to be induced in macrophages by inflammatory stimuli. The soluble CD100 (sCD100) reduces migration and expression of inflammatory cytokines in human monocytes and dendritic cells, as well as the intake of oxidized low-density lipoprotein (oxLDL) by human macrophages. Considering the importance of macrophages in Leishmania infection and the potential role of sCD100 in the modulation of macrophage phagocytosis and activation, we analyzed the expression and distribution of CD100 in murine macrophages and the effects of sCD100 on macrophage infection by Leishmania (Leishmania) amazonensis. Here we show that CD100 expression in murine macrophages increases after infection with Leishmania. sCD100 augments infection and phagocytosis of Leishmania (L.) amazonensis promastigotes by macrophages, an effect dependent on macrophage CD72 receptor. Besides, sCD100 enhances phagocytosis of zymosan particles and infection by Trypanosoma cruzi.