Mammalian Target of Rapamycin Inhibition in Trypanosoma cruzi-Infected Macrophages Leads to an Intracellular Profile That Is Detrimental for Infection

Molecular regulation of NLRP3 inflammasome activation during parasitic infection

Parasitic diseases are a serious global health concern, causing many common and severe infections, including Chagas disease, leishmaniasis, and schistosomiasis. The NLRP3 inflammasome belongs to the NLR (nucleotide-binding domain leucine-rich-repeat-containing proteins) family, which are cytosolic proteins playing key roles in the detection of pathogens. NLRP3 inflammasomes are activated in immune responses to Plasmodium, Leishmania, Toxoplasma gondii, Entamoeba histolytica, Trypanosoma cruzi, and other parasites. The role of NLRP3 is not fully understood, but it is a crucial component of the innate immune response to parasitic infections and its functions as a sensor triggering the inflammatory response to the invasive parasites. However, while this response can limit the parasites' growth, it can also result in potentially catastrophic host pathology. This makes it essential to understand how NLRP3 interacts with parasites to initiate the inflammatory response. Plasmodium hemozoin, Leishmania glycoconjugate lipophosphoglycan (LPG) and E. histolytica Gal/GalNAc lectin can stimulate NLRP3 activation, while the dense granule protein 9 (GRA9) of T. gondii has been shown to suppress it. Several other parasitic products also have diverse effects on NLRP3 activation. Understanding the mechanism of NLRP3 interaction with these products will help to develop advanced therapeutic approaches to treat parasitic diseases. This review summarizes current knowledge of the NLRP3 inflammasome's action on the immune response to parasitic infections and aims to determine the mechanisms through which parasitic molecules either activate or inhibit its action.

Exosomes derived from rapamycin-treated 4T1 breast cancer cells induced polarization of macrophages to M1 phenotype

M2 macrophages are the most prevalent type in the tumor microenvironment and their polarization to M1 type can be used as a potential cancer immunotherapy. Here, we investigated the role of tumor microenvironment and particularly purified exosomes in M2 to M1 macrophage polarization. Rapamycin treatment on triple-negative breast cancer cells (TNBC) was performed. Tumor cells-derived exosomes (called texosomes) were isolated and characterized using scanning electron microscopy, transmission electron microscopy, dynamic light scattering, high-performance liquid chromatography, Fourier transform infrared, and Western blot assays. M2 mouse peritoneal macrophages were treated with rapamycin or rapamycin-texosome. Then, M1/M2 phenotype-specific marker genes and proteins were measured to assess the degree of M2 to M1 polarization. Finally, nitric oxide (NO) production, phagocytosis, and efferocytosis assays were assessed to verify the functionality of the polarized macrophages. Purified rapamycin-texosomes significantly increased the expression of the M1 markers (Irf5, Nos2, and CD86) and decreased M2 markers (Arg, Ym1, and CD206). In addition, the levels of M1-specific cytokines tumor necrosis factor alpha and interleukin 1β (IL-1β) were increased, whereas the levels of M2 specific cytokines IL-10 and transforming growth factor beta were declined. Furthermore, texosome treatment increased NO concentration and phagocytosis and decreased efferocytosis indicating M1 polarization. These findings suggest rapamycin-texosomes can induce M2 to M1 macrophages polarization as a potential immunotherapy for TNBC.

Mitochondrial control of innate immune responses

Mitochondria are versatile organelles and essential components of numerous biological processes such as energy metabolism, signal transduction, and cell fate determination. In recent years, their critical roles in innate immunity have come to the forefront, highlighting impacts on pathogenic defense, tissue homeostasis, and degenerative diseases. This review offers an in-depth and comprehensive examination of the multifaceted mechanisms underlying the interactions between mitochondria and innate immune responses. We will delve into the roles of healthy mitochondria as platforms for signalosome assembly, the release of mitochondrial components as signaling messengers, and the regulation of signaling via mitophagy, particularly to cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) signaling and inflammasomes. Furthermore, the review will explore the impacts of mitochondrial proteins and metabolites on modulating innate immune responses, the polarization of innate immune cells, and their implications on infectious and inflammatory diseases.

mTOR signaling inhibition decreases lysosome migration and impairs the success of Trypanosoma cruzi infection and replication in cardiomyocytes

Chagas disease is caused by the parasite Trypanosoma cruzi (T. cruzi) and, among all the chronic manifestations of the disease, Chronic Chagas Cardiomyopathy (CCC) is the most severe outcome. Despite high burden and public health importance in Latin America, there is a gap in understanding the molecular mechanisms that results in CCC development. Previous studies showed that T. cruzi uses the host machinery for infection and replication, including the repurposing of the responses to intracellular infection such as mitochondrial activity, vacuolar membrane, and lysosomal activation in benefit of parasite infection and replication. One common signaling upstream to many responses to parasite infection is mTOR pathway, previous associated to several downstream cellular mechanisms including autophagy, mitophagy and lysosomal activation. Here, using human iPSC derived cardiomyocytes (hiPSCCM), we show the mTOR pathway is activated in hiPSCCM after T. cruzi infection, and the inhibition of mTOR with rapamycin reduced number of T. cruzi 48 h post infection (hpi). Rapamycin treatment also reduced lysosome migration from nuclei region to cell periphery resulting in less T. cruzi inside the parasitophorous vacuole (PV) in the first hour of infection. In addition, the number of parasites leaving the PV to the cytoplasm to replicate in later times of infection was also lower after rapamycin treatment. Altogether, our data suggest that host's mTOR activation concomitant with parasite infection modulates lysosome migration and that T. cruzi uses this mechanism to achieve infection and replication. Modulating this mechanism with rapamycin impaired the success of T. cruzi life cycle independent of mitophagy.

Induction of Autophagy by Ursolic Acid Promotes the Elimination of Trypanosoma cruzi Amastigotes From Macrophages and Cardiac Cells

Chagas disease, caused by the parasite Trypanosoma cruzi, is an infectious illness endemic to Latin America and still lacks an effective treatment for the chronic stage. In a previous study in our laboratory, we established the protective role of host autophagy in vivo during T. cruzi infection in mice and proposed this process as one of the mechanisms involved in the innate immune response against this parasite. In the search for an autophagy inducer that increases the anti-T. cruzi response in the host, we found ursolic acid (UA), a natural pentacyclic triterpene with many biological actions including autophagy induction. The aim of this work was to study the effect of UA on T. cruzi infection in vitro in the late infection stage, when the nests of intracellular parasites are forming, in both macrophages and cardiac cells. To test this effect, the cells were infected with T. cruzi for 24 h and then treated with UA (5–10 µM). The data showed that UA significantly decreased the number of amastigotes found in infected cells in comparison with non-treated cells. UA also induced the autophagy response in both macrophages and cardiac cells under the studied conditions, and the inhibition of this pathway during UA treatment restored the level of infection. Interestingly, LC3 protein, the main marker of autophagy, was recruited around amastigotes and the acidic probe LysoTracker localized with them, two key features of xenophagy. A direct cytotoxic effect of UA was also found on trypomastigotes of T. cruzi, whereas epimastigotes and amastigotes displayed more resistance to this drug at the studied concentrations. Taken together, these data showed that this natural compound reduces T. cruzi infection in the later stages by promoting parasite damage through the induction of autophagy. This action, in addition to the effect of this compound on trypomastigotes, points to UA as an interesting lead for Chagas disease treatment in the future.

Gasdermins in Innate Host Defense Against Entamoeba histolytica and Other Protozoan Parasites

Gasdermins (GSDMs) are a group of proteins that are cleaved by inflammatory caspases to induce pore formation in the plasma membrane to cause membrane permeabilization and lytic cell death or pyroptosis. All GSDMs share a conserved structure, containing a cytotoxic N-terminal (NT) pore-forming domain and a C-terminal (CT) repressor domain. Entamoeba histolytica (Eh) in contact with macrophages, triggers outside-in signaling to activate inflammatory caspase-4/1 via the noncanonical and canonical pathway to promote cleavage of gasdermin D (GSDMD). Cleavage of GSDMD removes the auto-inhibition that masks the active pore-forming NT domain in the full-length protein by interactions with GSDM-CT. The cleaved NT-GSDMD monomers then oligomerize to form pores in the plasma membrane to facilitate the release of IL-1β and IL-18 with a measured amount of pyroptosis. Pyroptosis is an effective way to counteract intracellular parasites, which exploit replicative niche to avoid killing. To date, most GSDMs have been verified to perform pore-forming activity and GSDMD-induced pyroptosis is rapidly emerging as a mechanism of anti-microbial host defence. Here, we review our comprehensive and current knowledge on the expression, activation, biological functions, and regulation of GSDMD cleavage with emphases on physiological scenario and related dysfunctions of each GSDM member as executioner of cell death, cytokine secretion and inflammation against Eh and other protozoan parasitic infections.

Predicting Blood Parasite Load and Influence of Expression of iNOS on the Effect Size of Clinical Laboratory Parameters in Acute Trypanosoma cruzi Infection With Different Inoculum Concentrations in C57BL/6 Mice

In Chagas disease, the initial responses of phagocyte-mediated innate immunity are strongly associated with the control of Trypanosoma cruzi and are mediated by various signaling pathways, including the inducible nitric oxide synthetase (iNOS) pathway. The clinical and laboratory manifestations of Chagas disease depend on the parasite–host relationship, i.e., the responsive capacity of the host immune system and the immunogenicity of the parasite. Here, we evaluated effect sizes in clinical and laboratory parameters mediated by acute infection with different concentrations of T. cruzi inoculum in mice immunosuppressed via iNOS pathway inactivation. Infection was induced in C57BL/6 wild-type and iNOS^-/- mice with the “Y” strain of T. cruzi at three inoculum concentrations (3 × 10², 3 × 10³, and 3 × 10⁴). Parasitemia and mortality in both mouse strains were monitored. Immunohistochemistry was performed to quantify amastigotes in cardiac tissues and cardiac musculature cells. Biochemical parameters, such as blood urea nitrogen, sodium, albumin, and globulin concentrations, among others, were measured, and cytokine concentrations were also measured. Effect sizes were determined by the eta squared formula. Compared with that in wild-type animals, mice with an absence of iNOS expression demonstrated a greater parasite load, with earlier infection and a delayed parasitemia peak. Inoculum concentration was positively related to death in the immunosuppressed subgroup. Nineteen parameters (hematological, biochemical, cytokine-related, and histopathological) in the immunocompetent subgroup and four in the immunosuppressed subgroup were associated with parasitemia. Parasitemia, biochemical parameters, and hematological parameters were found to be predictors in the knockout group. The impact of effect sizes on the markers evaluated based on T. cruzi inoculum concentration was notably high in the immunocompetent group (Cohen’s d = 88.50%; p <.001). These findings contribute to the understanding of physiopathogenic mechanisms underlying T. cruzi infection and also indicate the influence of the concentration of T. cruzi during infection and the immunosuppression through the iNOS pathway in clinical laboratory heterogeneity reported in acute Chagas disease.

Modulation of Macrophage Immunometabolism: A New Approach to Fight Infections

Macrophages are essential innate immune cells that contribute to host defense during infection. An important feature of macrophages is their ability to respond to extracellular cues and to adopt different phenotypes and functions in response to these stimuli. The evidence accumulated in the last decade has highlighted the crucial role of metabolic reprogramming during macrophage activation in infectious context. Thus, understanding and manipulation of macrophage immunometabolism during infection could be of interest to develop therapeutic strategies. In this review, we focus on 5 major metabolic pathways including glycolysis, pentose phosphate pathway, fatty acid oxidation and synthesis, tricarboxylic acid cycle and amino acid metabolism and discuss how they sustain and regulate macrophage immune function in response to parasitic, bacterial and viral infections as well as trained immunity. At the end, we assess whether some drugs including those used in clinic and in development can target macrophage immunometabolism for potential therapy during infection with an emphasis on SARS-CoV2 infection.

Transcriptomic Profile of Canine DH82 Macrophages Infected by Leishmania infantum Promastigotes with Different Virulence Behavior

Zoonotic visceral leishmaniosis caused by Leishmania infantum is an endemic disease in the Mediterranean Basin affecting mainly humans and dogs, the main reservoir. The leishmaniosis outbreak declared in the Community of Madrid (Spain) led to a significant increase in human disease incidence without enhancing canine leishmaniosis prevalence, suggesting a better adaptation of the outbreak's isolates by other host species. One of the isolates obtained in the focus, IPER/ES/2012/BOS1FL1 (BOS1FL1), has previously demonstrated a different phenotype than the reference strain MCAN/ES/1996/BCN150 (BCN150), characterized by a lower infectivity when interacting with canine macrophages. Nevertheless, not enough changes in the cell defensive response were found to support their different behavior. Thus, we decided to investigate the molecular mechanisms involved in the interaction of both parasites with DH82 canine macrophages by studying their transcriptomic profiles developed after infection using RNA sequencing. The results showed a common regulation induced by both parasites in the phosphoinositide-3-kinase-protein kinase B/Akt and NOD-like receptor signaling pathways. However, other pathways, such as phagocytosis and signal transduction, including tumor necrosis factor, mitogen-activated kinases and nuclear factor-κB, were only regulated after infection with BOS1FL1. These differences could contribute to the reduced infection ability of the outbreak isolates in canine cells. Our results open a new avenue to investigate the true role of adaptation of L. infantum isolates in their interaction with their different hosts.

Characterisation of Macrophage Polarisation in Mice Infected with Ninoa Strain of Trypanosoma cruzi

Macrophages (MΦ) play a key role in the development of the protective immune response against Trypanosoma cruzi infection. To determine the role of MΦ subtypes M1 and M2 in the development of immunity against the Mexican strain of T. cruzi (Ninoa strain), we have analysed in a time course the infection and characterised the M1 and M2 subtypes in two mouse models, BALB/c and C57BL/6. After infection, BALB/c mice developed an increased blood parasite load and the parasites were cleared from the blood one week later than in C57BL/6 mice. However, similar cellular infiltrate and cardiac alterations were observed between BALB/c and C57BL/6 mice. At 36 days, the T. cruzi infection differentially modulated the expression of immune cells, and both the BALB/c and C57BL/6 mice significantly reduced TCD4+ cells. However, BALB/c mice produced significantly more TCD8+ than C57BL/6 mice in the spleen and lymph nodes. Furthermore, BALB/c mice produce significantly more MΦ in the spleen, while C57BL/6 produce similar levels to uninfected mice. The M1 MΦ ratio increased significantly at 3-5 days post-infection (dpi), but then decreased slightly. On the contrary, the M2 MΦ were low at the beginning of the infection, but the proportion of M1 and M2 MΦ at 36 dpi was similar. Importantly, the MΦ subtypes M2c and M2d significantly increased the induction of tissue repair by the end of the acute phase of the infection. These results indicate that the Ninoa strain has developed strategies to modulate the immune response, with fine differences depending on the genetic background of the host.

Mitochondria as a Cellular Hub in Infection and Inflammation

Mitochondria are the energy center of the cell. They are found in the cell cytoplasm as dynamic networks where they adapt energy production based on the cell’s needs. They are also at the center of the proinflammatory response and have essential roles in the response against pathogenic infections. Mitochondria are a major site for production of Reactive Oxygen Species (ROS; or free radicals), which are essential to fight infection. However, excessive and uncontrolled production can become deleterious to the cell, leading to mitochondrial and tissue damage. Pathogens exploit the role of mitochondria during infection by affecting the oxidative phosphorylation mechanism (OXPHOS), mitochondrial network and disrupting the communication between the nucleus and the mitochondria. The role of mitochondria in these biological processes makes these organelle good targets for the development of therapeutic strategies. In this review, we presented a summary of the endosymbiotic origin of mitochondria and their involvement in the pathogen response, as well as the potential promising mitochondrial targets for the fight against infectious diseases and chronic inflammatory diseases.

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.

Pathogenic effects of inhibition of mTORC1/STAT3 axis facilitates Staphylococcus aureus-induced pyroptosis in human macrophages

BACKGROUND

Pyroptosis is a recently identified pathway of caspase-mediated cell death in response to microbes, lipopolysaccharide, or chemotherapy in certain types of cells. However, the mechanism of how pyroptosis is regulated is not well-established.

METHODS

Herein, the intracellular bacteria were detected by staining and laser confocal microscopy and TEM. Live/dead cell imaging assay was used to examine macrophage death. Western blot and immunohistochemical staining were used to examine the protein changes. IFA was used to identify typical budding vesicles of pyroptosis and the STAT3 nuclear localization. SEM was used to observe the morphological characteristics of pyroptosis. ELISA was used to detect the level of inflammatory cytokines. Pyroptosis was filmed in macrophages by LSCM.

RESULTS

S. aureus was internalized by human macrophages. Intracellular S. aureus induced macrophage death. S. aureus invasion increased the expression of NLRP3, Caspase1 (Casp-1 p20) and the accumulation of GSDMD-NT, GSDMD-NT pore structures, and the release of IL-1β and IL-18 in macrophages. Macrophages pyroptosis induced by S. aureus can be abrogated by blockage of S. aureus phagocytosis. The pyroptosic effect by S. aureus infection was promoted by either rapamycin or Stattic, a specific inhibitor for mTORC1 or STAT3. Inhibition of mTORC1 or STAT3 induced pyroptosis. mTORC1 regulated the pyroptosic gene expression through governing the nuclear localization of STAT3. mTORC1/STAT3 axis may play a regulatory role in pyroptosis within macrophages.

CONCLUSIONS

S. aureus infection induces human macrophage pyroptosis, inhibition of mTORC1/STAT3 axis facilitates S. aureus-induced pyroptosis. mTORC1 and STAT3 are associated with pyroptosis. Our findings demonstrate a regulatory function of the mTORC1/STAT3 axis in macrophage pyroptosis, constituting a novel mechanism by which pyroptosis is regulated in macrophages. Video Abstract Macrophages were infected with S. aureus for 3 h (MOI 25:1), and pyroptosis was filmed in macrophages by laser confocal microscopy. A representative field was recorded. Arrow indicates lysing dead cell.

Mitochondrial Reactive Oxygen Species: Double-Edged Weapon in Host Defense and Pathological Inflammation During Infection

Mitochondria are inevitable sources for the generation of mitochondrial reactive oxygen species (mtROS) due to their fundamental roles in respiration. mtROS were reported to be bactericidal weapons with an innate effector function during infection. However, the controlled generation of mtROS is vital for the induction of efficient immune responses because excessive production of mtROS with mitochondrial damage leads to sustained inflammation, resulting in pathological outcomes such as sepsis. Here, we discuss the beneficial and detrimental roles of mtROS in the innate immune system during bacterial, viral, and fungal infections. Recent evidence suggests that several pathogens have evolved multiple strategies to modulate mtROS for their own benefit. We are just beginning to understand the mechanisms by which mtROS generation is regulated and how mtROS affect protective and pathological responses during infection. Several agents/small molecules that prevent the uncontrolled production of mtROS are known to be beneficial in the maintenance of tissue homeostasis during sepsis. mtROS-targeted approaches need to be incorporated into preventive and therapeutic strategies against a variety of infections.

Inflammasome Activation in Response to Intracellular Protozoan Parasites

Inflammasomes are cytosolic complexes that assemble in response to cellular stress or upon sensing microbial molecules, culminating in cytokine processing and an inflammatory form of cell death called pyroptosis. Inflammasomes are usually composed of a sensor molecule, an adaptor protein, and an inflammatory caspase, such as Caspase-1, which cleaves and activates multiple substrates, including Gasdermin-D, pro-IL-1β, and pro-IL-18. Ultimately, inflammasome activation promotes inflammation and restriction of the microbial infection. In recent years, many studies have addressed the role of inflammasomes during fungal, bacterial, viral, and parasitic diseases, revealing sophisticated aspects of the host-pathogen interaction. In this review, we summarize recent advances on inflammasome activation in response to intracellular parasites, including Leishmania spp., Plasmodium spp., Trypanosoma cruzi, and Toxoplasma gondii.

Rapamycin Treatment Reduces Acute Myocarditis Induced by Trypanosoma cruzi Infection

Chagas disease affects millions of people mainly in Latin America and is a protozoan illness caused by the parasite Trypanosoma cruzi. Chagasic cardiomyopathy is the leading cause of mortality of infected patients, due to compromised electrical and mechanical cardiac function induced by tissue remodeling, especially fibrosis, and lymphocytic infiltration. Some cellular biochemical pathways can be protective to the heart, and we tested if the in vivo activation of the autophagic machinery by rapamycin could reduce parasite-induced myocarditis. Regarding the expression of LC3, an autophagy marker, we observed its upregulation in the cardiac tissue of infected untreated mice. However, after rapamycin treatment, an autophagy inducer, infected mice showed reduced electrical cardiac dysfunctions, myocarditis, cardiac damage, and reduced production of pro-inflammatory cytokines by the heart. On the other hand, the parasite's life cycle was not affected, and we observed no modulations in cardiac tissue or blood parasitemia. Our data indicate that, at least partially, autophagy induction controls inflammation in the heart¸ illustrating the complexity of the pathways that concur to the development of the infection.

Search of Allosteric Inhibitors and Associated Proteins of an AKT-like Kinase from Trypanosoma cruzi

Proteins associated to the PI3K/AKT/mTOR signaling pathway are widely used targets for cancer treatment, and in recent years they have also been evaluated as putative targets in trypanosomatids parasites, such as Trypanosoma cruzi. Here, we performed a virtual screening approach to find candidates that can bind regions on or near the Pleckstrin homology domain of an AKT-like protein in T. cruzi. The compounds were also evaluated in vitro. The in silico and experimental results allowed us to identify a set of compounds that can potentially alter the intracellular signaling pathway through the AKT-like kinase of the parasite; among them, a derivative of the pyrazolopyridine nucleus with an IC₅₀ of 14.25 ± 1.00 μM against amastigotes of T. cruzi. In addition, we built a protein–protein interaction network of T. cruzi to understand the role of the AKT-like protein in the parasite, and look for additional proteins that can be postulated as possible novel molecular targets for the rational design of compounds against T. cruzi.

Early Trypanosoma cruzi Infection Triggers mTORC1-Mediated Respiration Increase and Mitochondrial Biogenesis in Human Primary Cardiomyocytes

Chagasic chronic cardiomyopathy is one of the most frequent and severe manifestations of Chagas disease, caused by the parasite Trypanosoma cruzi. The pathogenic and biochemical mechanisms responsible for cardiac lesions remain not completely understood, although it is clear that hypertrophy and subsequent heart dilatation is in part caused by the direct infection of cardiomyocytes. In this work, we evaluated the initial response of human cardiomyocytes to T. cruzi infection by transcriptomic profiling. Immediately after infection, cardiomyocytes dramatically change their gene expression patterns, up regulating most of the genes encoding for respiratory chain, oxidative phosphorylation and protein synthesis. We found that these changes correlate with an increase in basal and maximal respiration, as well as in spare respiratory capacity, which is accompanied by mitochondrial biogenesis pgc-1α independent. We also demonstrate that these changes are mediated by mTORC1 and reversed by rapamycin, resembling the molecular mechanisms described for the non-chagasic hypertrophic cardiomyopathy. The results of the present work identify that early during infection, the activation of mTORC1, mitochondrial biogenesis and improvement in oxidative phosphorylation are key biochemical changes that provide new insights into the host response to parasite infection and the pathogenesis of chronic chagasic cardiomyopathy. The finding that this phenotype can be reversed opens a new perspective in the treatment of Chagas disease, through the identification of host targets, and the use of combined parasite and host targeted therapies, in order to prevent chagasic cardiomyopathy.