Trypanosoma cruzi induces edematogenic responses in mice and invades cardiomyocytes and endothelial cells in vitro by activating distinct kinin receptor (B1/B2) subtypes

Interaction of Angiotensin-(1-7) with kinins in the kidney circulation: Role of B1 receptors

Changes in renal hemodynamics impact renal function during physiological and pathological conditions. In this context, renal vascular resistance (RVR) is regulated by components of the Renin-Angiotensin System (RAS) and the Kallikrein-Kinin System (KKS). However, the interaction between these vasoactive peptides on RVR is still poorly understood. Here, we studied the crosstalk between angiotensin-(1-7) and kinins on RVR. The right kidneys of Wistar rats were isolated and perfused in a closed-circuit system. The perfusion pressure and renal perfusate flow were continuously monitored. Ang-(1-7) (1.0-25.0 nM) caused a sustained, dose-dependent reduction of relative RVR (rRVR). This phenomenon was sensitive to 10 nM A-779, a specific Mas receptor (MasR) antagonist. Bradykinin (BK) promoted a sustained and transient reduction in rRVR at 1.25 nM and 125 nM, respectively. The transient effect was abolished by 4 μM des-Arg9-Leu8-bradykinin (DALBK), a specific kinin B1 receptor (B1R) antagonist. Accordingly, des-Arg9-bradykinin (DABK) 1 μM (a B1R agonist) increased rRVR. Interestingly, pre-perfusion of Ang-(1-7) changed the sustained reduction of rRVR triggered by 1.25 nM BK into a transient effect. On the other hand, pre-perfusion of Ang-(1-7) primed and potentiated the DABK response, this mechanism being sensitive to A-779 and DALBK. Binding studies performed with CHO cells stably transfected with MasR, B1R, and kinin B2 receptor (B2R) showed no direct interaction between Ang-(1-7) with B1R or B2R. In conclusion, our findings suggest that Ang-(1-7) differentially modulates kinin's effect on RVR in isolated rat kidneys. These results help to expand the current knowledge regarding the crosstalk between the RAS and KKS complex network in RVR.

The ecotin-like peptidase inhibitor of Trypanosoma cruzi prevents TMPRSS2-PAR2-TLR4 crosstalk downmodulating infection and inflammation

Trypanosoma cruzi is the causative agent of Chagas disease, a chronic pathology that affects the heart and/or digestive system. This parasite invades and multiplies in virtually all nucleated cells, using a variety of host cell receptors for infection. T. cruzi has a gene that encodes an ecotin-like inhibitor of serine peptidases, ISP2. We generated ISP2-null mutants (Δisp2) in T. cruzi Dm28c using CRISPR/Cas9. Epimastigotes of Δisp2 grew normally in vitro but were more susceptible to lysis by human serum compared to parental and ISP2 add-back lines. Tissue culture trypomastigotes of Δisp2 were more infective to human muscle cells in vitro, which was reverted by the serine peptidase inhibitors aprotinin and camostat, suggesting that host cell epitheliasin/TMPRSS2 is the target of ISP2. Pretreatment of host cells with an antagonist to the protease-activated receptor 2 (PAR2) or an inhibitor of Toll-like receptor 4 (TLR4) selectively counteracted the increased cell invasion by Δisp2, but did not affect invasion by parental and add-back lines. The same was observed following targeted gene silencing of PAR2, TLR4 or TMPRSS2 in host cells by siRNA. Furthermore, Δisp2 caused increased tissue edema in a BALB/c mouse footpad infection model after 3 h differently to that observed following infection with parental and add-back lines. We propose that ISP2 contributes to protect T. cruzi from the anti-microbial effects of human serum and to prevent triggering of PAR2 and TLR4 in host cells, resulting in the modulation of host cell invasion and contributing to decrease inflammation during acute infection.

Genetic Ablation and Pharmacological Blockade of Bradykinin B1 Receptor Unveiled a Detrimental Role for the Kinin System in Chagas Disease Cardiomyopathy

Chagas disease, the parasitic infection caused by Trypanosoma cruzi, afflicts about 6 million people in Latin America. Here, we investigated the hypothesis that T. cruzi may fuel heart parasitism by activating B1R, a G protein-coupled (brady) kinin receptor whose expression is upregulated in inflamed tissues. Studies in WT and B1R^-/- mice showed that T. cruzi DNA levels (15 days post infection-dpi) were sharply reduced in the transgenic heart. FACS analysis revealed that frequencies of proinflammatory neutrophils and monocytes were diminished in B1R^-/- hearts whereas CK-MB activity (60 dpi) was exclusively detected in B1R^+/+ sera. Since chronic myocarditis and heart fibrosis (90 dpi) were markedly attenuated in the transgenic mice, we sought to determine whether a pharmacological blockade of the des-Arg⁹-bradykinin (DABK)/B1R pathway might alleviate chagasic cardiomyopathy. Using C57BL/6 mice acutely infected by a myotropic T. cruzi strain (Colombian), we found that daily treatment (15-60 dpi) with R-954 (B1R antagonist) reduced heart parasitism and blunted cardiac injury. Extending R-954 treatment to the chronic phase (120-160 dpi), we verified that B1R targeting (i) decreased mortality indexes, (ii) mitigated chronic myocarditis, and (iii) ameliorated heart conduction disturbances. Collectively, our study suggests that a pharmacological blockade of the proinflammatory KKS/DABK/B1R pathway is cardioprotective in acute and chronic Chagas disease.

Sheltered in Stromal Tissue Cells, Trypanosoma cruzi Orchestrates Inflammatory Neovascularization via Activation of the Mast Cell Chymase Pathway

Microangiopathy may worsen the clinical outcome of Chagas disease. Given the obstacles to investigating the dynamics of inflammation and angiogenesis in heart tissues parasitized by Trypanosoma cruzi, here we used intravital microscopy (IVM) to investigate microcirculatory alterations in the hamster cheek pouch (HCP) infected by green fluorescent protein-expressing T. cruzi (GFP-T. cruzi). IVM performed 3 days post-infection (3 dpi) consistently showed increased baseline levels of plasma extravasation. Illustrating the reciprocal benefits that microvascular leakage brings to the host-parasite relationship, these findings suggest that intracellular amastigotes, acting from inside out, stimulate angiogenesis while enhancing the delivery of plasma-borne nutrients and prosurvival factors to the infection foci. Using a computer-based analysis of images (3 dpi), we found that proangiogenic indexes were positively correlated with transcriptional levels of proinflammatory cytokines (pro-IL1β and IFN-γ). Intracellular GFP-parasites were targeted by delaying for 24 h the oral administration of the trypanocidal drug benznidazole. A classification algorithm showed that benznidazole (>24 h) blunted angiogenesis (7 dpi) in the HCP. Unbiased proteomics (3 dpi) combined to pharmacological targeting of chymase with two inhibitors (chymostatin and TY-51469) linked T. cruzi-induced neovascularization (7 dpi) to the proangiogenic activity of chymase, a serine protease stored in secretory granules from mast cells.

Update on relevant trypanosome peptidases: Validated targets and future challenges

Trypanosoma cruzi, the agent of the American Trypanosomiasis, Chagas disease, and Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense, the agents of Sleeping sickness (Human African Trypanosomiasis, HAT), as well as Trypanosoma brucei brucei, the agent of the cattle disease nagana, contain cysteine, serine, threonine, aspartyl and metallo peptidases. The most abundant among these enzymes are the cysteine proteases from the Clan CA, the Cathepsin L-like cruzipain and rhodesain, and the Cathepsin B-like enzymes, which have essential roles in the parasites and thus are potential targets for chemotherapy. In addition, several other proteases, present in one or both parasites, have been characterized, and some of them are also promising candidates for the developing of new drugs. Recently, new inhibitors, with good selectivity for the parasite proteasomes, have been described and are very promising as lead compounds for the development of new therapies for these neglected diseases. This article is part of a Special Issue entitled: "Play and interplay of proteases in health and disease".

The role of vascular endothelium and exosomes in human protozoan parasitic diseases

The vascular endothelium is a vital component in maintaining the structure and function of blood vessels. The endothelial cells (ECs) mediate vital regulatory functions such as the proliferation of cells, permeability of various tissue membranes, and exchange of gases, thrombolysis, blood flow, and homeostasis. The vascular endothelium also regulates inflammation and immune cell trafficking, and ECs serve as a replicative niche for many bacterial, viral, and protozoan infectious diseases. Endothelial dysfunction can lead to vasodilation and pro-inflammation, which are the hallmarks of many severe diseases. Exosomes are nanoscale membrane-bound vesicles that emerge from cells and serve as important extracellular components, which facilitate communication between cells and maintain homeostasis during normal and pathophysiological states. Exosomes are also involved in gene transfer, inflammation and antigen presentation, and mediation of the immune response during pathogenic states. Protozoa are a diverse group of unicellular organisms that cause many infectious diseases in humans. In this regard, it is becoming increasingly evident that many protozoan parasites (such as Plasmodium, Trypanosoma, Leishmania, and Toxoplasma) utilize exosomes for the transfer of their virulence factors and effector molecules into the host cells, which manipulate the host gene expression, immune responses, and other biological activities to establish and modulate infection. In this review, we discuss the role of the vascular endothelium and exosomes in and their contribution to pathogenesis in malaria, African sleeping sickness, Chagas disease, and leishmaniasis and toxoplasmosis with an emphasis on their actions on the innate and adaptive immune mechanisms of resistance.

Kinins and Their Receptors in Infectious Diseases

Kinins and their receptors have been implicated in a series of pathological alterations, representing attractive pharmacological targets for several diseases. The present review article aims to discuss the role of the kinin system in infectious diseases. Literature data provides compelling evidence about the participation of kinins in infections caused by diverse agents, including viral, bacterial, fungal, protozoan, and helminth-related ills. It is tempting to propose that modulation of kinin actions and production might be an adjuvant strategy for management of infection-related complications.

Kinins and nitric oxide in patients with chronic chagas disease and systemic arterial hypertension

BACKGROUND

Chronic Chagas disease (CCHD) associated with Systemic Arterial Hypertension (SAH) is frequently found in areas where the disease is endemic. The pathogenesis of patients with both pathologies (CCHD-SAH) is unsettled. Nitric Oxide (NO) and Kinins are important players in the myocardial inflammation process in experimental CCHD. No previous study has addressed this question in patients with CCHD, particularly in those with CCHD-SAH. Accordingly, this study was undertaken in an attempt to contribute to the understanding of the pathogenesis of patients with CCHD-SAH.

METHODS

Thirty-seven patients with a positive serology for Chagas disease were enrolled; 15 had CCHD alone, 22 had CCHD-SAH (abnormal ECG/Doppler echocardiogram plus a systolic blood pressure > 140 mmHg or diastolic blood pressure > 90 mmHg on admission), and 11 had SAH alone. Thirty healthy individuals matched by age and sex served as controls. Plasma High-molecular (Hkg) and low-molecular weight (LKg) kininogens, plasma kallikrein levels (Pkal and Tcal), Kininase II, and plasma NO were measured.

RESULTS

HKg and LKg were lower in CCHD-SAH patients in comparison with other groups (P < .0001). Pkal and Tcal were higher in CCHD-SAH patients in comparison with the other groups (P< .0001). Kininase II levels were similar in SAH, CCHD, and CCHD-SAH patients, but lower in comparison with controls (P< .0001). NO levels were similar in CCHD and CCHD-SAH patients, but higher in comparison with SAH patients and controls (P > .0001).

CONCLUSION

Such findings suggest increased Kinin and NO activity in patients with CCHD-SAH, thus contributing to the understanding of the pathogenesis of this condition.

Vismione B Interferes with Trypanosoma cruzi Infection of Vero Cells and Human Stem Cell-Derived Cardiomyocytes

Traditional African medicine is a source of new molecules that might be useful in modern therapeutics. We tested ten limonoids, six quinones, one xanthone, one alkaloid, and one cycloartane, isolated from four Cameroonian medicinal plants, and one plant-associated endophytic fungus, against Trypanosoma cruzi, the etiological agent of Chagas disease (CD). Vero cells, or human-induced pluripotent stem cells (hiPSC)-derived cardiomyocytes (hiPSC-CM) were infected with T. cruzi trypomastigotes (discrete typing unit types I or II). Infection took place in the presence of drugs, or 24 hours before drug treatment. Forty-eight hours after infection, infection rates and parasite multiplication were evaluated by Giemsa stain. Cell metabolism was measured to determine functional integrity. In Vero cells, several individual molecules significantly affected T. cruzi infection and multiplication with no, or minor, effects on cell viability. Reduced infection rates and multiplication by the quinone vismione B was superior to the commonly used therapeutic benznidazole (BNZ). The vismione B concentration inhibiting 50% of T. cruzi infection (IC₅₀) was 1.3 µM. When drug was applied after infection, anti-Trypanosoma effects of vismione B [10 µM) were significantly stronger than effects of BNZ (23 µM). Furthermore, in hiPSC-CM cultures, infection and multiplication rates in the presence of vismione B (10 µM) were significantly lower than in BNZ (11.5 µM), without showing signs of cytotoxicity. Our data indicate that vismione B is more potent against T. cruzi infection and multiplication than BNZ, with stronger effects on established infection. Vismione B, therefore, might become a promising lead molecule for treatment development for CD.

Potent and selective inhibitors for M32 metallocarboxypeptidases identified from high-throughput screening of anti-kinetoplastid chemical boxes

Enzymes of the M32 family are Zn-dependent metallocarboxypeptidases (MCPs) widely distributed among prokaryotic organisms and just a few eukaryotes including Trypanosoma brucei and Trypanosoma cruzi, the causative agents of sleeping sickness and Chagas disease, respectively. These enzymes are absent in humans and several functions have been proposed for trypanosomatid M32 MCPs. However, no synthetic inhibitors have been reported so far for these enzymes. Here, we present the identification of a set of inhibitors for TcMCP-1 and TbMCP-1 (two trypanosomatid M32 enzymes sharing 71% protein sequence identity) from the GlaxoSmithKline HAT and CHAGAS chemical boxes; two collections grouping 404 compounds with high antiparasitic potency, drug-likeness, structural diversity and scientific novelty. For this purpose, we adapted continuous fluorescent enzymatic assays to a medium-throughput format and carried out the screening of both collections, followed by the construction of dose-response curves for the most promising hits. As a result, 30 micromolar-range inhibitors were discovered for one or both enzymes. The best hit, TCMDC-143620, showed sub-micromolar affinity for TcMCP-1, inhibited TbMCP-1 in the low micromolar range and was inactive against angiotensin I-converting enzyme (ACE), a potential mammalian off-target structurally related to M32 MCPs. This is the first inhibitor reported for this family of MCPs and considering its potency and specificity, TCMDC-143620 seems to be a promissory starting point to develop more specific and potent chemical tools targeting M32 MCPs from trypanosomatid parasites.

Subverting bradykinin-evoked inflammation by co-opting the contact system: lessons from survival strategies of Trypanosoma cruzi

PURPOSE OF REVIEW

During Chagas disease, Trypanosoma cruzi alternates between intracellular and extracellular developmental forms. After presenting an overview about the roles of the contact system in immunity, I will review experimental studies showing that activation of the kallikrein-kinin system (KKS) translates into mutual benefits to the host/parasite relationship.

RECENT FINDINGS

T. cruzi trypomastigotes initiate inflammation by activating tissue-resident innate sentinel cells via the TLR2/CXCR2 pathway. Following neutrophil-evoked microvascular leakage, the parasite's major cysteine protease (cruzipain) cleaves plasma-borne kininogens and complement C5. Tightly regulated by angiotensin-converting enzyme (ACE), kinins and C5a in turn further propagate inflammation via iterative cycles of mast cell degranulation, contact system activation, bradykinin release and activation of endothelial bradykinin B2 receptors (B2R). Recently, studies in the intracardiac model of infection revealed a dichotomic role for bradykinin and endothelin-1: generated upon contact activation (mast cell/KKS pathway), these pro-oedematogenic peptides reciprocally stimulate trypomastigote invasion of heart cells that naturally overexpress B2R and endothelin receptors (ETaR/ETbR).

SUMMARY

Studies focusing on the immunopathogenesis of Chagas disease revealed that the contact system plays a dual role in host/parasite balance: T. cruzi co-opts bradykinin-induced plasma leakage as a strategy to increment heart parasitism and increase immune resistance by upregulating type-1 effector T-cell production in secondary lymphoid tissues.

Host-Directed Drug Therapies for Neglected Tropical Diseases Caused by Protozoan Parasites

The neglected tropical diseases (NTDs) caused by protozoan parasites are responsible for significant morbidity and mortality worldwide. Current treatments using anti-parasitic drugs are toxic and prolonged with poor patient compliance. In addition, emergence of drug-resistant parasites is increasing worldwide. Hence, there is a need for safer and better therapeutics for these infections. Host-directed therapy using drugs that target host pathways required for pathogen survival or its clearance is a promising approach for treating infections. This review will give a summary of the current status and advances of host-targeted therapies for treating NTDs caused by protozoa.

Pathogen interactions with endothelial cells and the induction of innate and adaptive immunity

There are over 10 trillion endothelial cells (EC) that line the vasculature of the human body. These cells not only have specialized functions in the maintenance of homeostasis within the circulation and various tissues but they also have a major role in immune function. EC also represent an important replicative niche for a subset of viral, bacterial, and parasitic organisms that are present in the blood or lymph; however, there are major gaps in our knowledge regarding how pathogens interact with EC and how this influences disease outcome. In this article, we review the literature on EC-pathogen interactions and their role in innate and adaptive mechanisms of resistance to infection and highlight opportunities to address prominent knowledge gaps.

G Protein-Coupled Kinin Receptors and Immunity Against Pathogens

For decades, immunologists have considered the complement system as a paradigm of a proteolytic cascade that, acting cooperatively with the immune system, enhances host defense against infectious organisms. In recent years, advances made in thrombosis research disclosed a functional link between activated neutrophils, monocytes, and platelet-driven thrombogenesis. Forging a physical barrier, the fibrin scaffolds generated by synergism between the extrinsic and intrinsic (contact) pathways of coagulation entrap microbes within microvessels, limiting the systemic spread of infection while enhancing the clearance of pathogens by activated leukocytes. Insight from mice models of thrombosis linked fibrin formation via the intrinsic pathway to the autoactivation of factor XII (FXII) by negatively charged "contact" substances, such as platelet-derived polyphosphates and DNA from neutrophil extracellular traps. Following cleavage by FXIIa, activated plasma kallikrein (PK) initiates inflammation by liberating the nonapeptide bradykinin (BK) from an internal domain of high molecular weight kininogen (HK). Acting as a paracrine mediator, BK induces vasodilation and increases microvascular permeability via activation of endothelial B2R, a constitutively expressed subtype of kinin receptor. During infection, neutrophil-driven extravasation of plasma fuels inflammation via extravascular activation of the kallikrein-kinin system (KKS). Whether liberated by plasma-borne PK, tissue kallikrein, and/or microbial-derived proteases, the short-lived kinins activate immature dendritic cells via B2R, thus linking the infection-associated innate immunity/inflammation to the adaptive arm of immunity. As inflammation persists, a GPI-linked carboxypeptidase M removes the C-terminal arginine from the primary kinin, converting the B2R agonist into a high-affinity ligand for B1R, a GPCR subtype that is transcriptionally upregulated in injured/inflamed tissues. As reviewed here, lessons taken from studies of kinin receptor function in experimental infections have shed light on the complex proteolytic circuits that, acting at the endothelial interface, reciprocally couple immunity to the proinflammatory KKS.

Mast Cell Coupling to the Kallikrein-Kinin System Fuels Intracardiac Parasitism and Worsens Heart Pathology in Experimental Chagas Disease

During the course of Chagas disease, infectious forms of Trypanosoma cruzi are occasionally liberated from parasitized heart cells. Studies performed with tissue culture trypomastigotes (TCTs, Dm28c strain) demonstrated that these parasites evoke neutrophil/CXCR2-dependent microvascular leakage by activating innate sentinel cells via toll-like receptor 2 (TLR2). Upon plasma extravasation, proteolytically derived kinins and C5a stimulate immunoprotective Th1 responses via cross-talk between bradykinin B2 receptors (B2Rs) and C5aR. Awareness that TCTs invade cardiovascular cells in vitro via interdependent activation of B2R and endothelin receptors [endothelin A receptor (ET_AR)/endothelin B receptor (ET_BR)] led us to hypothesize that T. cruzi might reciprocally benefit from the formation of infection-associated edema via activation of kallikrein-kinin system (KKS). Using intravital microscopy, here we first examined the functional interplay between mast cells (MCs) and the KKS by topically exposing the hamster cheek pouch (HCP) tissues to dextran sulfate (DXS), a potent "contact" activator of the KKS. Surprisingly, although DXS was inert for at least 30 min, a subtle MC-driven leakage resulted in factor XII (FXII)-dependent activation of the KKS, which then amplified inflammation via generation of bradykinin (BK). Guided by this mechanistic insight, we next exposed TCTs to "leaky" HCP-forged by low dose histamine application-and found that the proinflammatory phenotype of TCTs was boosted by BK generated via the MC/KKS pathway. Measurements of footpad edema in MC-deficient mice linked TCT-evoked inflammation to MC degranulation (upstream) and FXII-mediated generation of BK (downstream). We then inoculated TCTs intracardiacally in mice and found a striking decrease of parasite DNA (quantitative polymerase chain reaction; 3 d.p.i.) in the heart of MC-deficient mutant mice. Moreover, the intracardiac parasite load was significantly reduced in WT mice pretreated with (i) cromoglycate (MC stabilizer) (ii) infestin-4, a specific inhibitor of FXIIa (iii) HOE-140 (specific antagonist of B2R), and (iv) bosentan, a non-selective antagonist of ET_AR/ET_BR. Notably, histopathology of heart tissues from mice pretreated with these G protein-coupled receptors blockers revealed that myocarditis and heart fibrosis (30 d.p.i.) was markedly and redundantly attenuated. Collectively, our study suggests that inflammatory edema propagated via activation of the MC/KKS pathway fuels intracardiac parasitism by generating infection-stimulatory peptides (BK and endothelins) in the edematous heart tissues.

Mechanisms of Infectivity and Evasion Derived from Microvesicles Cargo Produced by Trypanosoma cruzi

Cell invasion by the intracellular protozoans requires interaction of proteins from both the host and the parasite. Many parasites establish chronic infections, showing they have the potential to escape the immune system; for example, Trypanosoma cruzi is an intracellular parasite that causes Chagas disease. Parasite internalization into host cell requires secreted and surface molecules, such as microvesicles. The release of microvesicles and other vesicles, such as exosomes, by different eukaryotic organisms was first observed in the late twentieth century. The characterization and function of these vesicles have recently been the focus of several investigations. In this review, we discuss the release of microvesicles by T. cruzi. The molecular content of these vesicles is composed of several molecules that take place during parasite-host cell interaction and contribute to the parasite-driven mechanism of evasion from the host immune system. These new findings appear to have a profound impact on the comprehension of T. cruzi biology and highlight novel potential strategies for developing more efficient therapeutic approaches.

Differential Expression of Inflammation-Related Genes in Children with Down Syndrome

OBJECTIVE

The aim of the study was to investigate the expression patterns of a specific set of genes involved in the inflammation process in children with Down Syndrome (DS) and children without the syndrome (control group) to identify differences that may be related to the immune abnormalities observed in DS individuals.

METHOD

RNA samples were obtained from peripheral blood, and gene expression was quantified using the TaqMan® Array Plate Human Inflammation Kit, which facilitated the investigation into 92 inflammation-related genes and four reference genes using real-time polymerase chain reaction (qPCR).

RESULTS

Twenty genes showed differential expression in children with DS; 12 were overexpressed (PLA2G2D, CACNA1D, ALOX12, VCAM1, ICAM1, PLCD1, ADRB1, HTR3A, PDE4C, CASP1, PLA2G5, and PLCB4), and eight were underexpressed (LTA4H, BDKRB1, ADRB2, CD40LG, ITGAM, TNFRSF1B, ITGB1, and TBXAS1). After statistically correcting for the false discovery rate, only the genes BDKRB1 and LTA4H showed differential expression, and both were underexpressed within the DS group.

CONCLUSION

DS children showed differential expression of inflammation-related genes that were not located on chromosome 21 compared with children without DS. The BDKRB1 and LTA4H genes may differentiate the case and control groups based on the inflammatory response, which plays an important role in DS pathogenesis.

Autoimmune pathogenesis of Chagas heart disease: looking back, looking ahead

Chagas heart disease is an inflammatory cardiomyopathy that develops in approximately one-third of individuals infected with the protozoan parasite Trypanosoma cruzi. Since the discovery of T. cruzi by Carlos Chagas >100 years ago, much has been learned about Chagas disease pathogenesis; however, the outcome of T. cruzi infection is highly variable and difficult to predict. Many mechanisms have been proposed to promote tissue inflammation, but the determinants and the relative importance of each have yet to be fully elucidated. The notion that some factor other than the parasite significantly contributes to the development of myocarditis was hypothesized by the first physician-scientists who noted the conspicuous absence of parasites in the hearts of those who succumbed to Chagas disease. One of these factors-autoimmunity-has been extensively studied for more than half a century. Although questions regarding the functional role of autoimmunity in the pathogenesis of Chagas disease remain unanswered, the development of autoimmune responses during infection clearly occurs in some individuals, and the implications that this autoimmunity may be pathogenic are significant. In this review, we summarize what is known about the pathogenesis of Chagas heart disease and conclude with a view of the future of Chagas disease diagnosis, pathogenesis, therapy, and prevention, emphasizing recent advances in these areas that aid in the management of Chagas disease.

Mammalian cellular culture models of Trypanosoma cruzi infection: a review of the published literature

Cellular culture infection with Trypanosoma cruzi is a tool used to dissect the biological mechanisms behind Chagas disease as well as to screen potential trypanocidal compounds. Data on these models are highly heterogeneous, which represents a challenge when attempting to compare different studies. The purpose of this review is to provide an overview of the cell culture infectivity assays performed to date. Scientific journal databases were searched for articles in which cultured cells were infected with any Trypanosoma cruzi strain or isolate regardless of the study’s goal. From these articles the cell type, parasite genotype, culture conditions and infectivity results were extracted. This review represents an initial step toward the unification of infectivity model data. Important differences were detected when comparing the pathophysiology of Chagas disease with the experimental conditions used in the analyzed studies. While Trypanosoma cruzi preferentially infects stromal cells in vivo, most of the assays employ epithelial cell lines. Furthermore, the most commonly used parasite strain (Tulahuen-TcVI) is associated with chagasic cardiomyopathy only in the Southern Cone of South America. Suggestions to overcome these discrepancies include the use of stromal cell lines and parasite genotypes associated with the known characteristics of the natural history of Chagas disease.

Endothelial transmigration by Trypanosoma cruzi

Chagas heart disease, the leading cause of heart failure in Latin America, results from infection with the parasite Trypanosoma cruzi. Although T. cruzi disseminates intravascularly, how the parasite contends with the endothelial barrier to escape the bloodstream and infect tissues has not been described. Understanding the interaction between T. cruzi and the vascular endothelium, likely a key step in parasite dissemination, could inform future therapies to interrupt disease pathogenesis. We adapted systems useful in the study of leukocyte transmigration to investigate both the occurrence of parasite transmigration and its determinants in vitro. Here we provide the first evidence that T. cruzi can rapidly migrate across endothelial cells by a mechanism that is distinct from productive infection and does not disrupt monolayer integrity or alter permeability. Our results show that this process is facilitated by a known modulator of cellular infection and vascular permeability, bradykinin, and can be augmented by the chemokine CCL2. These represent novel findings in our understanding of parasite dissemination, and may help identify new therapeutic strategies to limit the dissemination of the parasite.

Secreted proteases of Trypanosoma brucei gambiense: possible targets for sleeping sickness control?

Human African trypanosomiasis (HAT) is caused by trypanosomes of the species Trypanosoma brucei and belongs to the neglected tropical diseases. Presently, WHO has listed 36 countries as being endemic for sleeping sickness. No vaccine is available, and disease treatment is difficult and has life-threatening side effects. Therefore, there is a crucial need to search for new therapeutic targets against the parasite. Trypanosome excreted-secreted proteins could be promising targets, as the total secretome was shown to inhibit, in vitro, host dendritic cell maturation and their ability to induce lymphocytic allogenic responses. The secretome was found surprisingly rich in various proteins and unexpectedly rich in diverse peptidases, covering more than ten peptidase families or subfamilies. Given their abundance, one may speculate that they would play a genuine role not only in classical "housekeeping" tasks but also in pathogenesis. The paper reviews the deleterious role of proteases from trypanosomes, owing to their capacity to degrade host circulating or structural proteins, as well as proteic hormones, causing severe damage and preventing host immune response. In addition, proteases account for a number of drug targets, such drugs being used to treat severe diseases such AIDS. This review underlines the importance of secreted proteins and especially of secreted proteases as potential targets in HAT-fighting strategies. It points out the need to conduct further investigations on the specific role of each of these various proteases in order to identify those playing a central role in sleeping sickness and would be suitable for drug targeting.

Trypanosoma cruzi highjacks TrkC to enter cardiomyocytes and cardiac fibroblasts while exploiting TrkA for cardioprotection against oxidative stress

Chronic Chagas cardiomyopathy (CCC), caused by the obligate intracellular protozoan parasite Trypanosoma cruzi, is a major cause of morbidity and mortality in Latin America. CCC begins when T. cruzi enters cardiac cells for intracellular multiplication and differentiation, a process that starts with recognition of host-cell entry receptors. However, the nature of these surface molecules and corresponding parasite counter-receptor(s) is poorly understood. Here we show that antibodies against neurotrophin (NT) receptor TrkC, but not against family members TrkA and TrkB, prevent T. cruzi from invading primary cultures of cardiomyocytes and cardiac fibroblasts. Invasion is also selectively blocked by the TrkC ligand NT-3, and by antagonists of Trk autophosphorylation and downstream signalling. Therefore, these results indicate that T. cruzi gets inside cardiomyocytes and cardiac fibroblasts by activating TrkC preferentially over TrkA. Accordingly, short hairpin RNA interference of TrkC (shTrkC), but not TrkA, selectively prevents T. cruzi from entering cardiac cells. Additionally, T. cruzi parasite-derived neurotrophic factor (PDNF)/trans-sialidase, a TrkC-binding protein, but not family member gp85, blocks entry dose-dependently, underscoring the specificity of PDNF as TrkC counter-receptor in cardiac cell invasion. In contrast to invasion, competitive and shRNA inhibition studies demonstrate that T. cruzi-PDNF recognition of TrkA, but not TrkC on primary cardiomyocytes and the cardiomyocyte cell line H9c2 protects the cells against oxidative stress. Thus, this study shows that T. cruzi via PDNF favours neurotrophin receptor TrkC for cardiac cell entry and TrkA for cardiomyocyte protection against oxidative stress, and suggests a new therapeutic opportunity in PDNF and/or fragments thereof for CCC therapy as entry inhibitors and/or cardioprotection agonists.

The kallikrein-kinin system in experimental Chagas disease: a paradigm to investigate the impact of inflammatory edema on GPCR-mediated pathways of host cell invasion by Trypanosoma cruzi

Chronic chagasic myocarditis (CCM) depends on Trypanosoma cruzi persistence in the myocardium. Studies of the proteolytic mechanisms governing host/parasite balance in peripheral sites of T. cruzi infection revealed that tissue culture trypomastigotes (TCTs) elicit inflammatory edema and stimulate protective type-1 effector T cells through the activation of the kallikrein-kinin system. Molecular studies linked the proinflammatory phenotype of Dm28c TCTs to the synergistic activities of tGPI, a lipid anchor that functions as a Toll-like receptor 2 (TLR2) ligand, and cruzipain, a kinin-releasing cysteine protease. Analysis of the dynamics of inflammation revealed that TCTs activate innate sentinel cells via TLR2, releasing CXC chemokines, which in turn evoke neutrophil/CXCR2-dependent extravasation of plasma proteins, including high molecular weight kininogen (HK), in parasite-laden tissues. Further downstream, TCTs process surface bound HK, liberating lysyl-BK (LBK), which then propagates inflammatory edema via signaling of endothelial G-protein-coupled bradykinin B₂ receptors (BK₂R). Dm28 TCTs take advantage of the transient availability of infection-promoting peptides (e.g., bradykinin and endothelins) in inflamed tissues to invade cardiovascular cells via interdependent signaling of BKRs and endothelin receptors (ETRs). Herein we present a space-filling model whereby ceramide-enriched endocytic vesicles generated by the sphingomyelinase pathway might incorporate BK₂R and ETRs, which then trigger Ca²⁺-driven responses that optimize the housekeeping mechanism of plasma membrane repair from cell wounding. The hypothesis predicts that the NF-κB-inducible BKR (BK₁R) may integrate the multimolecular signaling platforms forged by ceramide rafts, as the chronic myocarditis progresses. Exploited as gateways for parasite invasion, BK₂R, BK₁R, ET_AR, ET_BR, and other G protein-coupled receptor partners may enable persistent myocardial parasitism in the edematous tissues at expense of adverse cardiac remodeling.

Current understanding of the Trypanosoma cruzi-cardiomyocyte interaction

Trypanosoma cruzi, the etiological agent of Chagas disease, exhibits multiple strategies to ensure its establishment and persistence in the host. Although this parasite has the ability to infect different organs, heart impairment is the most frequent clinical manifestation of the disease. Advances in knowledge of T. cruzi-cardiomyocyte interactions have contributed to a better understanding of the biological events involved in the pathogenesis of Chagas disease. This brief review focuses on the current understanding of molecules involved in T. cruzi-cardiomyocyte recognition, the mechanism of invasion, and on the effect of intracellular development of T. cruzi on the structural organization and molecular response of the target cell.

The enhanced permeability retention effect: a new paradigm for drug targeting in infection

Multidrug-resistant, Gram-negative infection is a major global determinant of morbidity, mortality and cost of care. The advent of nanomedicine has enabled tailored engineering of macromolecular constructs, permitting increasingly selective targeting, alteration of volume of distribution and activity/toxicity. Macromolecules tend to passively and preferentially accumulate at sites of enhanced vascular permeability and are then retained. This enhanced permeability and retention (EPR) effect, whilst recognized as a major breakthrough in anti-tumoral targeting, has not yet been fully exploited in infection. Shared pathophysiological pathways in both cancer and infection are evident and a number of novel nanomedicines have shown promise in selective, passive, size-mediated targeting to infection. This review describes the similarities and parallels in pathophysiological pathways at molecular, cellular and circulatory levels between inflammation/infection and cancer therapy, where use of this principle has been established.

Endothelin and bradykinin: 'brothers-in-arms' in Chagas vasculopathies?

Reports of Chagas disease are increasing in non-endemic populations across the globe. Apart from vector eradication and prevention efforts by public health organizations, current pharmacological interventions are sparse and show important side effects. In this issue of the BJP, Andrade et al. elegantly demonstrate a new pharmacological paradigm whereby Trypanosoma cruzi host cell invasion requires significant cross-talk between receptors for kinins and endothelins. It is shown, for example, that acting via both ET(A) and ET(B) receptors, endothelin-1 (ET-1) cooperates with the (TLR2/CXCR2/B(2) kinin receptor) complex to activate inflammatory processes in response to invading trypomastigotes. This study by Andrade et al. prompts, however, several important questions, summarized in this Commentary, such as the putative role of chymase-dependent production of ET-1, the contentious protective role of ACE inhibitors in Chagasic patients, the unexplored role of de novo formed B(1) receptors for kinins triggered by cytokines and the putative role of compartmentalized calcium pools in host cell invasion by trypomastigotes.

Trypanosoma cruzi invades host cells through the activation of endothelin and bradykinin receptors: a converging pathway leading to chagasic vasculopathy

BACKGROUND AND PURPOSE

Independent studies in experimental models of Trypanosoma cruzi appointed different roles for endothelin-1 (ET-1) and bradykinin (BK) in the immunopathogenesis of Chagas disease. Here, we addressed the hypothesis that pathogenic outcome is influenced by functional interplay between endothelin receptors (ET(A)R and ET(B)R) and bradykinin B(2) receptors (B(2)R).

EXPERIMENTAL APPROACH

Intravital microscopy was used to determine whether ETR/B(2)R drives the accumulation of rhodamine-labelled leucocytes in the hamster cheek pouch (HCP). Inflammatory oedema was measured in the infected BALB/c paw of mice. Parasite invasion was assessed in CHO over-expressing ETRs, mouse cardiomyocytes, endothelium (human umbilical vein endothelial cells) or smooth muscle cells (HSMCs), in the presence/absence of antagonists of B(2)R (HOE-140), ET(A)R (BQ-123) and ET(B)R (BQ-788), specific IgG antibodies to each GPCRs; cholesterol or calcium-depleting drugs. RNA interference (ET(A)R or ET(B)R genes) in parasite infectivity was investigated in HSMCs.

KEY RESULTS

BQ-123, BQ-788 and HOE-140 reduced leucocyte accumulation in HCP topically exposed to trypomastigotes and blocked inflammatory oedema in infected mice. Acting synergistically, ET(A)R and ET(B)R antagonists reduced parasite invasion of HSMCs to the same extent as HOE-140. Exogenous ET-1 potentiated T. cruzi uptake by HSMCs via ETRs/B(2)R, whereas RNA interference of ET(A)R and ET(B)R genes conversely reduced parasite internalization. ETRs/B(2)R-driven infection in HSMCs was reduced in HSMC pretreated with methyl-β-cyclodextrin, a cholesterol-depleting drug, or in thapsigargin- or verapamil-treated target cells.

CONCLUSIONS AND IMPLICATIONS

Our findings suggest that plasma leakage, a neutrophil-driven inflammatory response evoked by trypomastigotes via the kinin/endothelin pathways, may offer a window of opportunity for enhanced parasite invasion of cardiovascular cells.

Characterization of the M32 metallocarboxypeptidase of Trypanosoma brucei: differences and similarities with its orthologue in Trypanosoma cruzi

Metallocarboxypeptidases (MCP) of the M32 family of peptidases have been identified in a number of prokaryotic organisms but they are absent from eukaryotic genomes with the remarkable exception of those of trypanosomatids. The genome of Trypanosoma brucei, the causative agent of Sleeping Sickness, encodes one such MCP which displays 72% identity to the characterized TcMCP-1 from Trypanosoma cruzi. As its orthologue, TcMCP-1, Trypanosoma brucei MCP is a cytosolic enzyme expressed in both major stages of the parasite. Purified recombinant TbMCP-1 exhibits a significant hydrolytic activity against the carboxypeptidase B substrate FA (furylacryloil)-Ala-Lys at pH 7.0-7.8 resembling the T. cruzi enzyme. Several divalent cations had little effect on TbMCP-1 activity but increasing amounts of Co(2+) inhibited the enzyme. Despite having similar tertiary structure, both protozoan MCPs display different substrate specificity with respect to P1 position. Thus, TcMCP-1 enzyme cleaved Abz-FVK-(Dnp)-OH substrate (where Abz: o-aminobenzoic acid and Dnp: 2,4-dinitrophenyl) whereas TbMCP-1 had no activity on this substrate. Comparative homology models and sequence alignments using TcMCP-1 as a template led us to map several residues that could explain this difference. To verify this hypothesis, site-directed mutagenesis was undertaken replacing the TbMCP-1 residues by those present in TcMCP-1. We found that the substitution A414M led TbMCP-1 to gain activity on Abz-FVK-(Dnp)-OH, thus showing that this residue is involved in specificity determination, probably being part of the S1 sub-site. Moreover, the activity of both protozoan MCPs was explored on two vasoactive compounds such as bradykinin and angiotensin I resulting in two different hydrolysis patterns.

Infection-associated vasculopathy in experimental chagas disease pathogenic roles of endothelin and kinin pathways

Acting at the interface between microcirculation and immunity, Trypanosoma cruzi induces modifications in peripheral tissues which translate into mutual benefits to host/parasite balance. In this chapter, we will review evidence linking infection-associated vasculopathy to the proinflammatory activity of a small subset of T. cruzi molecules, namely GPI-linked mucins, cysteine proteases (cruzipain), surface glycoproteins of the trans-sialidase family and/or parasite-derived eicosanoids (thromboxane A(2)). Initial insight into pathogenesis came from research in animal models showing that myocardial fibrosis is worsened as result of endothelin upregulation by infected cardiovascular cells. Paralleling these studies, the kinin system emerged as a proteolytic mechanism that links oedematogenic inflammation to immunity. Analyses of the dynamics of inflammation revealed that tissue culture trypomastigotes elicit interstitial oedema in peripheral sites of infection through synergistic activation of toll-like 2 receptors (TLR2) and G-protein-coupled bradykinin receptors, respectively, engaged by tGPI (TLR2 ligand) and kinin peptides (bradykinin B2 receptors (BK(2)R) ligands) proteolytically generated by cruzipain. Further downstream, kinins stimulate lymph node dendritic cells via G-protein-coupled BK(2)R, thus converting these specialized antigen-presenting cells into T(H)1 inducers. Tightly regulated by angiotensin-converting enzyme, the intact kinins (BK(2)R agonists) may be processed by carboxypeptidase M/N, generating [des-Arg]-kinins, which activates BK(1)R, a subtype of GPCR that is upregulated by cardiovascular cells during inflammation. Ongoing studies may clarify if discrepancies between proinflammatory phenotypes of T. cruzi strains may be ascribed, at least in part, to variable expression of TLR2 ligands and cruzipain isoforms.

Mechanisms of host cell invasion by Trypanosoma cruzi

One of the more accepted concepts in our understanding of the biology of early Trypanosoma cruzi-host cell interactions is that the mammalian-infective trypomastigote forms of the parasite must transit the host cell lysosomal compartment in order to establish a productive intracellular infection. The acidic environment of the lysosome provides the appropriate conditions for parasite-mediated disruption of the parasitophorous vacuole and release of T. cruzi into the host cell cytosol, where replication of intracellular amastigotes occurs. Recent findings indicate a level of redundancy in the lysosome-targeting process where T. cruzi trypomastigotes exploit different cellular pathways to access host cell lysosomes in non-professional phagocytic cells. In addition, the reversible nature of the host cell penetration process was recently demonstrated when conditions for fusion of the nascent parasite vacuole with the host endosomal-lysosomal system were not met. Thus, the concept of parasite retention as a critical component of the T. cruzi invasion process was introduced. Although it is clear that host cell recognition, attachment and signalling are required to initiate invasion, integration of this knowledge with our understanding of the different routes of parasite entry is largely lacking. In this chapter, we focus on current knowledge of the cellular pathways exploited by T. cruzi trypomastigotes to invade non-professional phagocytic cells and to gain access to the host cell lysosome compartment.

Tumour necrosis factor (TNF)-mediated NF-κB activation facilitates cellular invasion of non-professional phagocytic epithelial cell lines by Trypanosoma cruzi

At the site of infection, pro-inflammatory cytokines locally produced by macrophages infected with Trypanosoma cruzi can activate surrounding non-professional phagocytes such as fibroblasts, epithelial and endothelial cells, which can be further invaded by the parasite. The effect of secreted soluble factors on the invasion of these cells remains, however, to be established. We show here that two epithelial cell lines become significantly susceptible to the infection by the Y strain of T. cruzi after tumour necrosis factor (TNF) treatment. The increase in the invasion was correlated with the increasing concentration of recombinant TNF added to cultures of HEK293T or LLC-MK2 cells. Supernatants taken from PMA-differentiated human monocytes infected with T. cruzi also increased the permissiveness of epithelial cells to subsequent infection with the parasite, which was inhibited by a TNF monoclonal antibody. Furthermore, the permissiveness induced by TNF was inhibited by TPCK, and led to significant decrease in the number of intracellular parasites, providing evidence that activation of NF-κB induced by TNF favours the invasion of the epithelial cell lines by T. cruzi through yet an unidentified mechanism. Our data indicate that soluble factors released from macrophages early in the infection favours T. cruzi invasion of non-professional phagocytic cells.

Pathogenesis of chagas' disease: parasite persistence and autoimmunity

Acute Trypanosoma cruzi infections can be asymptomatic, but chronically infected individuals can die of Chagas' disease. The transfer of the parasite mitochondrial kinetoplast DNA (kDNA) minicircle to the genome of chagasic patients can explain the pathogenesis of the disease; in cases of Chagas' disease with evident cardiomyopathy, the kDNA minicircles integrate mainly into retrotransposons at several chromosomes, but the minicircles are also detected in coding regions of genes that regulate cell growth, differentiation, and immune responses. An accurate evaluation of the role played by the genotype alterations in the autoimmune rejection of self-tissues in Chagas' disease is achieved with the cross-kingdom chicken model system, which is refractory to T. cruzi infections. The inoculation of T. cruzi into embryonated eggs prior to incubation generates parasite-free chicks, which retain the kDNA minicircle sequence mainly in the macrochromosome coding genes. Crossbreeding transfers the kDNA mutations to the chicken progeny. The kDNA-mutated chickens develop severe cardiomyopathy in adult life and die of heart failure. The phenotyping of the lesions revealed that cytotoxic CD45, CD8(+) γδ, and CD8α(+) T lymphocytes carry out the rejection of the chicken heart. These results suggest that the inflammatory cardiomyopathy of Chagas' disease is a genetically driven autoimmune disease.

The peptidases of Trypanosoma cruzi: digestive enzymes, virulence factors, and mediators of autophagy and programmed cell death

Trypanosoma cruzi, the agent of the American Trypanosomiasis, Chagas disease, contains cysteine, serine, threonine, aspartyl and metallo peptidases. The most abundant among these enzymes is cruzipain, a cysteine proteinase expressed as a mixture of isoforms, some of them membrane-bound. The enzyme is an immunodominant antigen in human chronic Chagas disease and seems to be important in the host/parasite relationship. Inhibitors of cruzipain kill the parasite and cure infected mice, thus validating the enzyme as a very promising target for the development of new drugs against the disease. In addition, a 30kDa cathepsin B-like enzyme, two metacaspases and two autophagins have been described. Serine peptidases described in the parasite include oligopeptidase B, a member of the prolyl oligopeptidase family involved in Ca(2+)-signaling during mammalian cell invasion; a prolyl endopeptidase (Tc80), against which inhibitors are being developed, and a lysosomal serine carboxypeptidase. Metallopeptidases homologous to the gp63 of Leishmania spp. are present, as well as two metallocarboxypeptidases belonging to the M32 family, previously found only in prokaryotes. The proteasome has properties similar to those of other eukaryotes, and its inhibition by lactacystin blocks some differentiation steps in the life cycle of the parasite. This article is part of a Special Issue entitled: Proteolysis 50 years after the discovery of lysosome.

Trypanosoma cruzi utilizes the host low density lipoprotein receptor in invasion

Background

Trypanosoma cruzi, an intracellular protozoan parasite that infects humans and other mammalian hosts, is the etiologic agent in Chagas disease. This parasite can invade a wide variety of mammalian cells. The mechanism(s) by which T. cruzi invades its host cell is not completely understood. The activation of many signaling receptors during invasion has been reported; however, the exact mechanism by which parasites cross the host cell membrane barrier and trigger fusion of the parasitophorous vacuole with lysosomes is not understood.

Methodology/Principal Findings

In order to explore the role of the Low Density Lipoprotein receptor (LDLr) in T. cruzi invasion, we evaluated LDLr parasite interactions using immunoblot and immunofluorescence (IFA) techniques. These experiments demonstrated that T. cruzi infection increases LDLr levels in infected host cells, inhibition or disruption of LDLr reduces parasite load in infected cells, T. cruzi directly binds recombinant LDLr, and LDLr-dependent T. cruzi invasion requires PIP2/3. qPCR analysis demonstrated a massive increase in LDLr mRNA (8000 fold) in the heart of T. cruzi infected mice, which is observed as early as 15 days after infection. IFA shows a co-localization of both LDL and LDLr with parasites in infected heart.

Conclusions/Significance

These data highlight, for the first time, that LDLr is involved in host cell invasion by this parasite and the subsequent fusion of the parasitophorous vacuole with the host cell lysosomal compartment. The model suggested by this study unifies previous models of host cell invasion for this pathogenic protozoon. Overall, these data indicate that T. cruzi targets LDLr and its family members during invasion. Binding to LDL likely facilitates parasite entry into host cells. The observations in this report suggest that therapeutic strategies based on the interaction of T. cruzi and the LDLr pathway should be pursued as possible targets to modify the pathogenesis of disease following infection.

Trypanosoma cruzi, an intracellular protozoan parasite that causes Chagas disease in humans and results in the development of cardiomyopathy, is a major health problem in endemic areas. This parasite can invade a wide variety of mammalian cells. The mechanisms by which these parasites invade their host cells are not completely understood. Our study highlights, for the first time, that the Low Density Lipoprotein receptor (LDLr) is important in the invasion and the subsequent fusion of the parasitophorous vacuole with host lysosomes. We demonstrate that T. cruzi directly binds to LDLr, and inhibition or disruption of LDLr significantly decreases parasite entry. Additionally, we have determined that this cross-linking triggers the accumulation of LDLr and phosphotidylinositol phosphates in coated pits, which initiates a signaling cascade that results in the recruitment of lysosomes, possibly via the sorting motif in the cytoplasmic tail of LDLr, to the site of adhesion/invasion. Studies of infected CD1 mice demonstrate that LDLs accumulate in infected heart and that LDLr co-localize with internalized parasites. Overall, this study demonstrates that LDLr and its family members, engaged mainly in lipoprotein transportation, are also involved in T. cruzi entry into host cells and this interaction likely contributes to the progression of chronic cardiomyopathy.

Captopril increases the intensity of monocyte infection by Trypanosoma cruzi and induces human T helper type 17 cells

The anti-hypertensive drug captopril is used commonly to reduce blood pressure of patients with severe forms of Chagas disease, a cardiomyopathy caused by chronic infection with the intracellular protozoan Trypanosoma cruzi. Captopril acts by inhibiting angiotensin-converting enzyme (ACE), the vasopressor metallopeptidase that generates angiotensin II and promotes the degradation of bradykinin (BK). Recent studies in mice models of Chagas disease indicated that captopril can potentiate the T helper type 1 (Th1)-directing natural adjuvant property of BK. Equipped with kinin-releasing cysteine proteases, T. cruzi trypomastigotes were shown previously to invade non-professional phagocytic cells, such as human endothelial cells and murine cardiomyocytes, through the signalling of G protein-coupled bradykinin receptors (B(2) KR). Monocytes are also parasitized by T. cruzi and these cells are known to be important for the host immune response during infection. Here we showed that captopril increases the intensity of T. cruzi infection of human monocytes in vitro. The increased parasitism was accompanied by up-regulated expression of ACE in human monocytes. While T. cruzi infection increased the expression of interleukin (IL)-10 by monocytes significantly, compared to uninfected cells, T. cruzi infection in association with captopril down-modulated IL-10 expression by the monocytes. Surprisingly, studies with peripheral blood mononuclear cells revealed that addition of the ACE inhibitor in association with T. cruzi increased expression of IL-17 by CD4(+) T cells in a B(2) KR-dependent manner. Collectively, our results suggest that captopril might interfere with host-parasite equilibrium by enhancing infection of monocytes, decreasing the expression of the modulatory cytokine IL-10, while guiding development of the proinflammatory Th17 subset.

Molecular mechanisms of host cell invasion by Trypanosoma cruzi

The protozoan parasite Trypanosoma cruzi, the etiologic agent of Chagas disease, is an obligate intracellular protozoan pathogen. Overlapping mechanisms ensure successful infection, yet the relationship between these cellular events and clinical disease remains obscure. This review explores the process of cell invasion from the perspective of cell surface interactions, intracellular signaling, modulation of the host cytoskeleton and endosomal compartment, and the intracellular innate immune response to infection.

Innate and Acquired Immunity in the Pathogenesis of Chagas Disease

The apparent discrepancy between the intensity of inflammatory reaction and scarce number of parasites in chronic chagasic myocarditis prompt several investigators to hypothesize that an autoimmune process was involved in the pathogenesis of Chagas disease. Here, we recapitulate diverse molecular and cellular mechanisms of innate and acquired immunity involved in the control of parasite replication and in the build up of myocarditis observed during infection with Trypanosoma cruzi. In addition, we review the immunoregulatory mechanisms responsible for preventing excessive immune response elicited by this protozoan parasite. Ongoing studies in this research area may provide novel therapeutic strategies that could enhance the immunoprotective response while preventing the deleterious parasite-elicited responses observed during Chagas disease.

Characterization of a 21kDa protein from Trypanosoma cruzi associated with mammalian cell invasion

Trypanosoma cruzi genomic database was screened for hypothetical proteins that showed high probability of being secreted or membrane anchored and thus, likely involved in host-cell invasion. A sequence that codes for a 21kDa protein that showed high probability of being secreted was selected. After cloning this protein sequence, the results showed that it was a ubiquitous protein and secreted by extracellular amastigotes. The recombinant form (P21-His(6)) adhered to HeLa cells in a dose-dependent manner. Pretreatment of host cells with P21-His(6) inhibited cell invasion by extracellular amastigotes from G and CL strains. On the other hand, when the protein was added to host cells at the same time as amastigotes, an increase in cell invasion was observed. Host-cell pretreatment with P21-His(6) augmented invasion by metacyclic trypomastigotes. Moreover, polyclonal antibody anti-P21 inhibited invasion only by extracellular amastigotes and metacyclic trypomastigotes from G strain. These results suggested that P21 might be involved in T. cruzi cell invasion. We hypothesize that P21 could be secreted in the juxtaposition parasite-host cell and triggers signaling events yet unknown that lead to parasite internalization.

Proteolytic generation of kinins in tissues infected by Trypanosoma cruzi depends on CXC chemokine secretion by macrophages activated via Toll-like 2 receptors

Previous analysis of the endogenous innate signals that steer T cell-dependent immunity in mice acutely infected by the protozoan Trypanosoma cruzi revealed that bradykinin (BK) or lysyl-BK, i.e., the short-lived peptides excised from plasma-borne kininogens through the activity of cruzipain, induces dendritic cell maturation via BK B(2) receptors (B(2)R). Here, we used the s.c. model of T. cruzi infection to study the functional interplay of TLR2, CXCR2, and B(2)R in edema development. Using intravital microscopy, we found that repertaxin (CXCR2 antagonist) blocked tissue-culture trypomastigotes (TCT)-induced plasma leakage and leukocyte accumulation in the hamster cheek pouch topically exposed to TCT. Furthermore, we found that TCT-evoked paw edema in BALB/c mice was blocked by repertaxin or HOE-140 (B(2)R antagonist), suggesting that CXCR2 propels the extravascular activation of the kinin/B(2)R pathway. We then asked if TLR2-mediated sensing of TCT by innate sentinel cells could induce secretion of CXC chemokines, which would then evoke neutrophil-dependent plasma leakage via the CXCR2/B(2)R pathway. Consistent with this notion, in vitro studies revealed that TCT induce robust secretion of CXC chemokines by resident macrophages in a TLR2-dependent manner. In contrast, TLR2(+/+) macrophages stimulated with insect-derived metacyclic trypomastigotes or epimastigotes, which lack the developmentally regulated TLR2 agonist displayed by TCT, failed to secrete keratinocyte-derived chemokine/MIP-2. Collectively, these results suggest that secretion of CXC chemokines by innate sentinel cells links TLR2-dependent recognition of TCT to the kinin system, a proteolytic web that potently amplifies vascular inflammation and innate immunity through the extravascular release of BK.

Perspectives on the Trypanosoma cruzi-host cell receptor interactions

Chagas disease is caused by the parasite Trypanosoma cruzi. The critical initial event is the interaction of the trypomastigote form of the parasite with host receptors. This review highlights recent observations concerning these interactions. Some of the key receptors considered are those for thromboxane, bradykinin, and for the nerve growth factor TrKA. Other important receptors such as galectin-3, thrombospondin, and laminin are also discussed. Investigation into the molecular biology and cell biology of host receptors for T. cruzi may provide novel therapeutic targets.

Angiotensin-converting enzyme limits inflammation elicited by Trypanosoma cruzi cysteine proteases: a peripheral mechanism regulating adaptive immunity via the innate kinin pathway

Tissue injury by pathogens induces a stereotyped inflammatory response that alerts the innate immune system of the potential threat to host integrity. Here, we review knowledge emerging from investigations of the role of the kinin system in the mechanisms that link innate to the adaptive phase of immunity. Progress in this field started with results demonstrating that bradykinin is an endogenous danger signal that induces dendritic cell (DC) maturation via G protein-coupled bradykinin B2 receptors (B2R). The immunostimulatory role of kinins was recently confirmed in two different mouse models of Trypanosoma cruzi infection, a parasitic protozoan equipped with kinin-releasing cysteine proteases (cruzipain). Infection by the intraperitoneal route showed that DCs from B2R-/- mice (susceptible phenotype) failed to sense kinin 'danger' signals proteolytically released by parasites, explaining why these mutant mice display lower frequencies of interferon-gamma-producing effector T-cells. Studies of the dynamics of inflammation in the subcutaneous model of infection revealed that the balance between cruzipain and angiotensin-converting enzyme, respectively acting as kinin-generating and degrading enzymes, governs extent of DC maturation and TH1 development via the B2R-dependent innate pathway. Studies of the kinin role in immunity may shed light on the relationship between proteolytic networks and the cytokine circuits that guide T-cell development.

Chagas heart disease pathogenesis: one mechanism or many?

Chagas heart disease (CHD), caused by the protozoan parasite Trypanosoma cruzi, is the leading cause of infectious myocarditis in the world. The etiology of CHD is unclear and multiple mechanisms have been proposed to explain the pathogenesis of the disease. This review describes the proposed mechanisms of CHD pathogenesis and evaluates the historical significance and evidence supporting each. Although the majority of CHD-related pathologies are currently attributed to parasite persistence in the myocardium and autoimmunity, there is strong evidence that CHD develops as a result of additive and even synergistic effects of several distinct mechanisms rather than one factor.

All Trypanosoma cruzi developmental forms present lysosome-related organelles

Trypanosoma cruzi epimastigote forms concentrate their major protease, cruzipain, in the same compartment where these parasites store macromolecules obtained from medium and for this ability these organelles were named as reservosomes. Intracellular digestion occurs mainly inside reservosomes and seems to be modulated by cruzipain and its natural inhibitor chagasin that also concentrates in reservosomes. T. cruzi mammalian forms, trypomastigotes and amastigotes, are unable to capture macromolecules by endocytosis, but also express cruzipain and chagasin, whose role in infectivity has been described. In this paper, we demonstrate that trypomastigotes and amastigotes also concentrate cruzipain, chagasin as well as serine carboxypeptidase in hydrolase-rich compartments of acidic nature. The presence of P-type proton ATPase indicates that this compartment is acidified by the same enzyme as epimastigote endocytic compartments. Electron microscopy analyzes showed that these organelles are placed at the posterior region of the parasite body, are single membrane bound and possess an electron-dense matrix with electronlucent inclusions. Three-dimensional reconstruction showed that these compartments have different size and shape in trypomastigotes and amastigotes. Based on these evidences, we suggest that all T. cruzi developmental stages present lysosome-related organelles that in epimastigotes have the additional and unique ability of storing cargo.

Roles of naturally occurring protease inhibitors in the modulation of host cell signaling and cellular invasion by Trypanosoma cruzi

Trypanosoma cruzi trypomastigotes rely on the structural diversity of the cruzipain family of cysteine proteases to infect and multiply in nonprofessional phagocytic cells. Herein, we will review studies demonstrating that the interplay of cruzipain with peptidase inhibitors modulate infection outcome in a variety of experimental settings. Studies with a panel of T. cruzi strains showed that parasite ability to invade human smooth muscle cells is influenced by the balance between cruzipain and chagasin, a tight binding endogenous inhibitor of papain-like cysteine proteases. Analysis of T. cruzi interaction with endothelial cells and cardiomyocytes indicated that parasite-induced activation of bradykinin receptors drive host cell invasion by [Ca2+]I-dependent pathways. Clues about the mechanisms underlying kinin generation in vivo by trypomastigotes came from analysis of the dynamics of edematogenic inflammation. Owing to plasma extravasation, the blood-borne kininogens accumulate in peripheral sites of infection. Upon diffusion in peripheral tissues, kininogens (i.e., type III cystatins) bind to heparan sulphate chains, thus constraining interactions of the cystatin-like inhibitory domains with cruzipain. The cell bound kininogens are then turned into facile substrates for cruzipain, which liberates kinins in peripheral tissues. Subjected to tight-regulation by kinin-degrading metallopeptidases, such as angiotensin converting enzyme, the short-lived kinin peptides play a dual role in the host-parasite balance. Rather than unilaterally stimulating pathogen infectivity via bradykinin receptors, the released kinins potently induce dendritic cell maturation, thus stimulating type 1 immune responses. In conclusion, the studies reviewed herein illustrate how regulation of parasite proteases may affect host-parasite equilibrium in the course of IT cruzi infection.

Kininogens Coordinate Adaptive Immunity through the Proteolytic Release of Bradykinin, an Endogenous Danger Signal Driving Dendritic Cell Maturation

Strategically positioned in peripheral tissues, immune sentinel cells sense microbes and/or their shed products through different types of pattern-recognition receptors. Upon secretion, pre-formed pro-inflammatory mediators activate the microvasculature, inducing endothelium/neutrophil adherence and impairing endothelium barrier function. As plasma proteins enter into peripheral tissues, short-lived proinflammatory peptides are rapidly generated by limited proteolysis of complement components and the kininogens (i.e. kinin-precursor proteins). While much emphasis has been placed on the studies of the vascular functions of kinins, their innate effector roles remain virtually unknown. A few years ago, we reported that exogenous bradykinin (BK) potently induces dendritic cell (DC) maturation, driving IL-12-dependent Th1 responses through the activation of G-protein-coupled BK B(2) receptors (B(2)R). The premise that immature DC might sense kinin-releasing pathogens through B(2)R was demonstrated in the subcutaneous mouse model of Trypanosoma cruzi infection. Analysis of the dynamics of parasite-evoked inflammation revealed that activation of TLR2/neutrophils drives the influx of plasma proteins, including kininogens, into peripheral tissues. Once associated to cell surfaces and/or extracellular matrices, the surface-bound kininogens are cleaved by T. cruzi cysteine proteases. Acting as short-lived 'danger' signals, kinins activate DC via B(2)R, converting them into Th1 inducers. Fine tuned control of the extravascular levels of these natural peptide adjuvants is exerted by kinin-degrading metallopeptidases, e.g. Angiotensin converting enzyme (ACE/CD143). In summary, the studies in the subcutaneous model of T. cruzi infection revealed that the peripheral levels of BK, a DC maturation signal, are controlled by TLR2/neutrophils and ACE, respectively characterized as positive and negative modulators of innate/adaptive immunity.