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

Leishmania donovani Induces Multiple Dynamic Responses in the Metabolome Associated with Amastigote Differentiation and Maturation Inside the Human Macrophage

Leishmania donovani infection of macrophages drives profound changes in the metabolism of both the host macrophage and the parasite, which undergoes different phases of development culminating in replication and propagation. However, the dynamics of this parasite-macrophage cometabolome are poorly understood. In this study, a multiplatform metabolomics pipeline combining untargeted, high-resolution CE-TOF/MS and LC-QTOF/MS with targeted LC-QqQ/MS was followed to characterize the metabolome alterations induced in L. donovani-infected human monocyte-derived macrophages from different donors at 12, 36, and 72 h post-infection. The set of alterations known to occur during Leishmania infection of macrophages, substantially expanded in this investigation, characterized the dynamics of the glycerophospholipid, sphingolipid, purine, pentose phosphate, glycolytic, TCA, and amino acid metabolism. Our results showed that only citrulline, arginine, and glutamine exhibited constant trends across all studied infection time points, while most metabolite alterations underwent a partial recovery during amastigote maturation. We determined a major metabolite response pointing to an early induction of sphingomyelinase and phospholipase activities and correlated with amino acid depletion. These data represent a comprehensive overview of the metabolome alterations occurring during promastigote-to-amastigote differentiation and maturation of L. donovani inside macrophages that contributes to our understanding of the relationship between L. donovani pathogenesis and metabolic dysregulation.

Upregulation of IL-33, CCL2, and CXCL16 levels in Brazilian pregnant women infected by Toxoplasma gondii

Congenital toxoplasmosis can cause neurological and eye damage, behavioral alterations, or death in fetuses or babies born to Toxoplasma gondii-infected women. Several pieces of evidence suggest that socioeconomic, environmental, and inflammatory patterns linked to the maternal immune response partly drive the pathogenesis of this disease. However, immunoregulation induced by T. gondii infection during gestation is not completely understood. The aim of this study was to assess the association between T. gondii seropositivity and concentrations of plasma markers (CCL2, CXCL16, IL-17, and IL-33) in Brazilian pregnant women. Inflammatory markers were measured by immunoassays in the plasma of 131 pregnant women (13 to 46 years old). The prevalence of T. gondii infections was 45.8% (n = 60) in this population. The concentrations of CCL2, CXCL16, and IL-33 were higher in T. gondii-seropositive than in seronegative pregnant women, while the opposite was observed for IL-17 levels. In IgG+ women, a strong correlation between IL-17 and IL-33 (r = 0.7508, p = 0.0001) and a moderate correlation between CXCL16/IL-17 (r = 0.7319, p = 0.0001) and CXCL16/CCL2 (r = 0.3519, p = 0.0098) was observed. In uninfected women, a strong correlation was found between IL-17 and CXCL16 (r = 0.6779, p = 0.0001) but moderate between IL-17 and IL-33 (r = 0.4820, p = 0.0001). In summary, our data suggest that plasma upregulation of CCL2, CXCL16, and IL-33 might exert a potential protective role in the mother/fetus/parasite axis and, in addition, multiparous women are more likely to be infected with T. gondii than primiparous women.

Role of Chemokines in the Pathogenesis of Visceral Leishmaniasis

Abstract:

Visceral leishmaniasis (VL; also known as kala-azar), caused by the protozoan parasite Leishmania donovani is characterized by the inability of the host to generate an effective immune response. The manifestations of the disease depends on involvement of various immune components such as activation of macrophages, cell mediated immunity, secretion of cytokines and chemokines, etc. Macrophages are the final host cells for Leishmania parasites to multiply, and they are the key to a controlled or aggravated response that leads to clinical symptoms. The two most common macrophage phenotypes are M1 and M2. The pro-inflammatory microenvironment (mainly by IL-1β, IL-6, IL-12, IL-23, and TNF-α cytokines) and tissue injury driven by classically activated macrophages (M1-like) and wound healing driven by alternatively activated macrophages (M2-like) in an anti-inflammatory environment (mainly by IL-10, TGF-β, chemokine ligand (CCL)1, CCL2, CCL17, CCL18, and CCL22). Moreover, on polarized Th cells, chemokine receptors are expressed differently. Typically, CXCR3 and CCR5 are preferentially expressed on polarized Th1 cells, whereas CCR3, CCR4 and CCR8 have been associated with the Th2 phenotype. Further, the ability of the host to produce a cell-mediated immune response capable of regulating and/or eliminating the parasite is critical in the fight against the disease. Here, we review the interactions between parasites and chemokines and chemokines receptors in the pathogenesis of VL.

Prognostic and pathogenic role of CXC Motif Ligand 16 in sepsis

Chemokine CXC motif ligand 16 (CXCL16) is an important mediator that has been shown to participate in various human diseases. The role of CXCL16 in the immunopathology of sepsis remains unidentified. In this study, we found that human patients with sepsis had significantly higher soluble levels of serum CXCL16 than healthy volunteers on day of intensive care unit (ICU) admission. Soluble CXCL16 remained significantly up-regulated in the patients with sepsis, which correlated with disease severity. Furthermore, nonsurvivors displayed significantly higher admission levels of soluble CXCL16 compared with survivors of septic patients. Soluble CXCL16 levels revealed significant prognostic value for 28-day mortality, and CXCL16 was shown to be an independent predictor of 28-day mortality in the patients with sepsis. In a murine model of cecal ligation and puncture (CLP)-induced nonsevere sepsis, supplementation of recombinant CXCL16 protein could increase sepsis-induced mortality and tissue injury. Conversely, neutralizing CXCL16 by anti-CXCL16 monoclonal antibody could decrease mortality and tissue injury in CLP-induced severe sepsis. However, CXCL16 did not affect the ability of these mice to clear bacteria in CLP. Taken together, CXCL16 could be related to sepsis not only as a novel biomarker of prognosis, but also as a potential target for therapeutic intervention.

The host mTOR pathway and parasitic diseases pathogenesis

The mechanistic (or mammalian) target of rapamycin (mTOR) is considered as a critical regulatory enzyme involved in essential signaling pathways affecting cell growth, cell proliferation, protein translation, regulation of cellular metabolism, and cytoskeletal structure. Also, mTOR signaling has crucial roles in cell homeostasis via processes such as autophagy. Autophagy prevents many pathogen infections and is involved on immunosurveillance and pathogenesis. Immune responses and autophagy are therefore key host responses and both are linked by complex mTOR regulatory mechanisms. In recent years, the mTOR pathway has been highlighted in different diseases such as diabetes, cancer, and infectious and parasitic diseases including leishmaniasis, toxoplasmosis, and malaria. The current review underlines the implications of mTOR signals and intricate networks on pathogen infections and the modulation of this master regulator by parasites. Parasitic infections are able to induce dynamic metabolic reprogramming leading to mTOR alterations in spite of many other ways impacting this regulatory network. Accordingly, the identification of parasite effects and interactions over such a complex modulation might reveal novel information regarding the biology of the abovementioned parasites and might allow the development of therapeutic strategies against parasitic diseases. In this sense, the effects of inhibiting the mTOR pathways are also considered in this context in the light of their potential for the prevention and treatment of parasitic diseases.

Translational profiling of macrophages infected with Leishmania donovani identifies mTOR- and eIF4A-sensitive immune-related transcripts

The protozoan parasite Leishmania donovani (L. donovani) causes visceral leishmaniasis, a chronic infection which is fatal when untreated. Herein, we investigated whether in addition to altering transcription, L. donovani modulates host mRNA translation to establish a successful infection. Polysome-profiling revealed that one third of protein-coding mRNAs expressed in primary mouse macrophages are differentially translated upon infection with L. donovani promastigotes or amastigotes. Gene ontology analysis identified key biological processes enriched for translationally regulated mRNAs and were predicted to be either activated (e.g. chromatin remodeling and RNA metabolism) or inhibited (e.g. intracellular trafficking and antigen presentation) upon infection. Mechanistic in silico and biochemical analyses showed selective activation mTOR- and eIF4A-dependent mRNA translation, including transcripts encoding central regulators of mRNA turnover and inflammation (i.e. PABPC1, EIF2AK2, and TGF-β). L. donovani survival within macrophages was favored under mTOR inhibition but was dampened by pharmacological blockade of eIF4A. Overall, this study uncovers a vast yet selective reprogramming of the host cell translational landscape early during L. donovani infection, and suggests that some of these changes are involved in host defense mechanisms while others are part of parasite-driven survival strategies. Further in vitro and in vivo investigation will shed light on the contribution of mTOR- and eIF4A-dependent translational programs to the outcome of visceral leishmaniasis.

MicroRNA exporter HuR clears the internalized pathogens by promoting pro-inflammatory response in infected macrophages

HuR is a miRNA derepressor protein that can act as miRNA sponge for specific miRNAs to negate their action on target mRNAs. Here we have identified how HuR, by inducing extracellular vesicles‐mediated export of miRNAs, ensures robust derepression of miRNA‐repressed cytokines essential for strong pro‐inflammatory response in activated mammalian macrophages. Leishmania donovani, the causative agent of visceral leishmaniasis, on the contrary alters immune response of the host macrophage by a variety of complex mechanisms to promote anti‐inflammatory response essential for the survival of the parasite. We have found that during Leishmania infection, the pathogen targets HuR to promote onset of anti‐inflammatory response in mammalian macrophages. In infected macrophages, Leishmania also upregulate protein phosphatase 2A that acts on Ago2 protein to keep it in dephosphorylated and miRNA‐associated form. This causes robust repression of the miRNA‐targeted pro‐inflammatory cytokines to establish an anti‐inflammatory response in infected macrophages. HuR has an inhibitory effect on protein phosphatase 2A expression, and mathematical modelling of macrophage activation process supports antagonistic miRNA‐modulatory roles of HuR and protein phosphatase 2A which mutually balances immune response in macrophage by targeting miRNA function. Supporting this model, ectopic expression of the protein HuR and simultaneous inhibition of protein phosphatase 2A induce strong pro‐inflammatory response in the host macrophage to prevent the virulent antimonial drug‐sensitive or drug‐resistant form of L. donovani infection. Thus, HuR can act as a balancing factor of immune responses to curtail the macrophage infection process by the protozoan parasite.