Congenital Transmission of Trypanosoma cruzi in Naturally Infected Dogs

Background: Congenital transmission (CT) of Trypanosoma cruzi in dogs has not been clearly demonstrated, even though dogs are important reservoirs of this agent. Materials and Methods: Seventeen late pregnant dogs seropositive for T. cruzi were selected, and a total of 84 fetuses were obtained. Blood and heart tissues from the fetuses and dams, and placental tissue from dam were collected. All tissues were analyzed by quantitative polymerase chain reaction (qPCR) for T. cruzi DNA (TcDNA) and inflammatory infiltrate and pathology by histological examination. CT was determined when physical, histological, or molecular evidence of T. cruzi was detected in blood or tissues of the fetuses. Results: A general transmission frequency of 59% was found, and 0.20 ± 0.24 of fetuses per litter were infected. Dams that were qPCR positive for TcDNA in cardiac tissue or blood displayed a transmission frequency of 100% and 67%, respectively. The highest parasite burden was noted in dams that were positive for TcDNA in both blood (82E-01 ± 1.54E-01) and cardiac (5.28E+03 ± 8.85E+03) tissues. In fetuses, higher parasitic burden in blood and cardiac tissue was found in those carried by dams that were seropositive and qPCR positive for TcDNA in cardiac tissue and blood. No amastigote nests were recorded in the cardiac tissue of fetuses in the histopathological studies, but typical lesions of T. cruzi infection were identified in all fetuses where CT occurred. Conclusions: CT of T. cruzi occurred at a high frequency in naturally infected pregnant dogs from the endemic areas.

Acute muscle mass loss was alleviated with HMGB1 neutralizing antibody treatment in severe burned rats

Burn injury is associated with muscle wasting, though the involved signaling mechanisms are not well understood. In this study, we aimed to examine the role of high mobility group box 1 (HMGB1) in signaling hyper-inflammation and consequent skeletal muscle impairment after burn. Sprague Dawley rats were randomly assigned into three groups: (1) sham burn, (2) burn, (3) burn/treatment. Animals in group 2 and group 3 received scald burn on 30% of total body surface area (TBSA) and immediately treated with chicken IgY and anti-HMGB1 antibody, respectively. Muscle tissues and other samples were collected at 3-days after burn. Body mass and wet/dry weights of the hind limb muscles (total and individually) were substantially decreased in burn rats. Acute burn provoked the mitochondrial stress and cell death and enhanced the protein ubiquitination and LC3A/B levels that are involved in protein degradation in muscle tissues. Further, an increase in muscle inflammatory infiltrate associated with increased differentiation, maturation and proinflammatory activation of bone marrow myeloid cells and αβ CD4+ T and γδ T lymphocytes was noted in in circulation and spleen of burn rats. Treatment with one dose of HMGB1 neutralizing antibody reduced the burn wound size and preserved the wet/dry weights of the hind limb muscles associated with a control in the markers of cell death and autophagy pathways in burn rats. Further, anti-HMGB1 antibody inhibited the myeloid and T cells inflammatory activation and subsequent dysregulated inflammatory infiltrate in the muscle tissues of burn rats. We conclude that neutralization of HMGB1-dependent proteolytic and inflammatory responses has potential beneficial effects in preventing the muscle loss after severe burn injury.

Effects of Acute and Chronic Trypanosoma cruzi Infection on Pregnancy Outcomes in Mice: Parasite Transmission, Mortality, Delayed Growth, and Organ Damage in Pups

Chagas disease is caused by Trypanosoma cruzi. This study aimed to determine the effects of T. cruzi infection on fertility rate and health of the newborn pups in pregnant mice. Female mice were challenged with T. cruzi and mated at 21 days (acute parasitemic phase) or 90 days (chronic parasite persistence phase) after infection. Pups were examined for growth up to 20 days after birth; and parasite burden in brain, heart, skeletal muscle, and intestine was measured by real-time quantitative PCR. The inflammatory infiltrate, necrosis, and fibrosis in pups' heart and brain tissues were evaluated by histology. T. cruzi infection in dams delayed the onset of pregnancy, decreased the fertility rate, and led to vertical transmission of parasite to the pups. Furthermore, infected dams delivered pups that exhibited decreased survival rate, decreased birth weight, and decreased growth rate. Significantly increased inflammation, necrosis, and fibrosis of cardiac and brain tissues were noted in pups born to infected dams. Initial challenge with higher parasite dose had more detrimental effects on fertility rate and pups' health in both acutely and chronically infected dams. In conclusion, mice offer a promising model to evaluate the efficacy of new vaccines and therapeutic drugs in controlling the acute and chronic maternal T. cruzi infection and congenital transmission to newborns, and in improving the fertility rate and pups' health outcomes.

Animal Models of Trypanosoma cruzi Congenital Transmission

Chagas disease, initiated by the etiological agent Trypanosoma cruzi, is an endemic infection in the American continent. Although vectorial transmission of T. cruzi is recognized as the main mode of infection, other routes such as congenital and blood transfusion are also documented as important methods of transmission. T. cruzi maternal–fetal transmission has been recorded in humans and examined by some investigators in naturally and experimentally infected mammals. Dogs are recognized as the major reservoir host in maintaining the domestic transmission of T. cruzi; however, the importance of congenital transmission in preserving the infection cycle in dogs has not been studied in detail. In this article, we reviewed the current knowledge of congenital transmission of T. cruzi in humans and compared the placental architecture of humans and different animals with particular attention to rodents, dogs, and non-human primates that have been used as experimental models of T. cruzi infection, congenital transmission, and Chagas disease pathogenesis. The placentas of humans and animals have some similar and dissimilar characteristics that should inform the study design and interpretation of results when evaluating the efficacy of new anti-parasite drugs and therapies against congenital infection.

Platelets, Macrophages, and Thromboinflammation in Chagas Disease

Chagas disease (CD) is a major health problem in the Americas and an emerging health problem in Europe and other nonendemic countries. Several studies have documented persistence of the protozoan parasite Trypanosoma cruzi, and oxidative and inflammatory stress are major pathogenic factor. Mural and cardiac thrombi, cardiac arrhythmias, and cardiomyopathy are major clinical features of CD. During T. cruzi infection, parasite-released factors induce endothelial dysfunction along with platelet (PLT) and immune-cell activation. PLTs have a fundamental role in maintaining hemostasis and preventing bleeding after vascular injury. Excessive activation of PLTs and coagulation cascade can result in thrombosis and thromboembolic events, which are recognized to occur in seropositive individuals in early stages of CD when clinically symptomatic heart disease is not apparent. Several host and parasite factors have been identified to signal hypercoagulability and increase the risk of ischemic stroke in early phases of CD. Further, PLT interaction with immune cells and their role in host defense against pathogens and inflammatory processes have only recently been recognized and evolving. In the context of parasitic diseases, PLTs function in directly responding to T. cruzi infection, and PLT interactions with immune cells in shaping the proinflammatory or immunoregulatory function of monocytes, macrophages, and neutrophils remains elusive. How T. cruzi infection alters systemic microenvironment conditions to influence PLT and immune-cell interactions is not understood. In this review, we discuss the current literature, and extrapolate the mechanistic situations to explain how PLT and innate immune cell (especially monocytes and macrophages) interactions might be sustaining hypercoagulability and thromboinflammation in chronic CD.

RBFOX2 is critical for maintaining alternative polyadenylation patterns and mitochondrial health in rat myoblasts

RBFOX2, which has a well-established role in alternative splicing, is linked to heart diseases. However, it is unclear whether RBFOX2 has other roles in RNA processing that can influence gene expression in muscle cells, contributing to heart disease. Here, we employ both 3'-end and nanopore cDNA sequencing to reveal a previously unrecognized role for RBFOX2 in maintaining alternative polyadenylation (APA) signatures in myoblasts. RBFOX2-mediated APA modulates mRNA levels and/or isoform expression of a collection of genes, including contractile and mitochondrial genes. Depletion of RBFOX2 adversely affects mitochondrial health in myoblasts, correlating with disrupted APA of mitochondrial gene Slc25a4. Mechanistically, RBFOX2 regulation of Slc25a4 APA is mediated through consensus RBFOX2 binding motifs near the distal polyadenylation site, enforcing the use of the proximal polyadenylation site. In sum, our results unveil a role for RBFOX2 in fine-tuning expression of mitochondrial and contractile genes via APA in myoblasts relevant to heart diseases.

Poly(ADP-ribose) polymerase 1 regulates mitochondrial DNA repair in an NAD-dependent manner

Mitochondrial DNA is located in organelle that house essential metabolic reactions and contains high reactive oxygen species. Therefore, mitochondrial DNA suffers more oxidative damage than its nuclear counterpart. Formation of a repair enzyme complex is beneficial to DNA repair. Recent studies have shown that mitochondrial DNA polymerase (Pol γ) and poly(ADP-ribose) polymerase 1 (PARP1) were found in the same complex along with other mitochondrial DNA repair enzymes, and mitochondrial PARP1 level is correlated with mtDNA integrity. However, the molecular basis for the functional connection between Pol γ and PARP1 has not yet been elucidated because cellular functions of PARP1 in DNA repair are intertwined with metabolism via NAD+ (nicotinamide adenosine dinucleotide), the substrate of PARP1, and a metabolic cofactor. To dissect the direct effect of PARP1 on mtDNA from the secondary perturbation of metabolism, we report here biochemical studies that recapitulated Pol γ PARylation observed in cells and showed that PARP1 regulates Pol γ activity during DNA repair in a metabolic cofactor NAD⁺ (nicotinamide adenosine dinucleotide)-dependent manner. In the absence of NAD⁺, PARP1 completely inhibits Pol γ, while increasing NAD⁺ levels to a physiological concentration that enables Pol γ to resume maximum repair activity. Because cellular NAD+ levels are linked to metabolism and to ATP production via oxidative phosphorylation, our results suggest that mtDNA damage repair is coupled to cellular metabolic state and the integrity of the respiratory chain.

Potential Role of Antioxidants as Adjunctive Therapy in Chagas Disease

Chagas disease (CD) is one of the most important neglected tropical diseases in the American continent. Host-derived nitroxidative stress in response to Trypanosoma cruzi infection can induce tissue damage contributing to the progression of Chagas disease. Antioxidant supplementation has been suggested as adjuvant therapy to current treatment. In this article, we synthesize and discuss the current evidence regarding the use of antioxidants as adjunctive compounds to fight harmful reactive oxygen species and lower the tissue oxidative damage during progression of chronic Chagas disease. Several antioxidants evaluated in recent studies have shown potential benefits for the control of oxidative stress in the host's tissues. Melatonin, resveratrol, the combination of vitamin C/vitamin E (vitC/vitE) or curcumin/benznidazole, and mitochondria-targeted antioxidants seem to be beneficial in reducing plasma and cardiac levels of lipid peroxidation products. Nevertheless, further research is needed to validate beneficial effects of antioxidant therapies in Chagas disease.

Genes of the cGMP-PKG-Ca2+ signaling pathway are alternatively spliced in cardiomyopathy: Role of RBFOX2

Aberrations in the cGMP-PKG-Ca2+ pathway are implicated in cardiovascular complications of diverse etiologies, though involved molecular mechanisms are not understood. We performed RNA-Seq analysis to profile global changes in gene expression and exon splicing in Chagas disease (ChD) murine myocardium. Ingenuity-Pathway-Analysis of transcriptome dataset identified 26 differentially expressed genes associated with increased mobilization and cellular levels of Ca2+ in ChD hearts. Mixture-of-isoforms and Enrichr KEGG pathway analyses of the RNA-Seq datasets from ChD (this study) and diabetic (previous study) murine hearts identified alternative splicing (AS) in eleven genes (Arhgef10, Atp2b1, Atp2a3, Cacna1c, Itpr1, Mef2a, Mef2d, Pde2a, Plcb1, Plcb4, and Ppp1r12a) of the cGMP-PKG-Ca2+ pathway in diseased hearts. AS of these genes was validated by an exon exclusion-inclusion assay. Further, Arhgef10, Atp2b1, Mef2a, Mef2d, Plcb1, and Ppp1r12a genes consisted RBFOX2 (RNA-binding protein) binding-site clusters, determined by analyzing the RBFOX2 CLIP-Seq dataset. H9c2 rat heart cells transfected with Rbfox2 (vs. scrambled) siRNA confirmed that expression of Rbfox2 is essential for proper exon splicing of genes of the cGMP-PKG-Ca2+ pathway. We conclude that changes in gene expression may influence the Ca2+ mobilization pathway in ChD, and AS impacts the genes involved in cGMP/PKG/Ca2+ signaling pathway in ChD and diabetes. Our findings suggest that ChD patients with diabetes may be at increased risk of cardiomyopathy and heart failure and provide novel ways to restore cGMP-PKG regulated signaling networks via correcting splicing patterns of key factors using oligonucleotide-based therapies for the treatment of cardiovascular complications.

Epidemiology and pathogenesis of maternal-fetal transmission of Trypanosoma cruzi and a case for vaccine development against congenital Chagas disease

Trypanos o ma cruzi (T. cruzi or Tc) is the causative agent of Chagas disease (CD). It is common for patients to suffer from non-specific symptoms or be clinically asymptomatic with acute and chronic conditions acquired through various routes of transmission. The expecting women and their fetuses are vulnerable to congenital transmission of Tc. Pregnant women face formidable health challenges because the frontline antiparasitic drugs, benznidazole and nifurtimox, are contraindicated during pregnancy. However, it is worthwhile to highlight that newborns can be cured if they are diagnosed and given treatment in a timely manner. In this review, we discuss the pathogenesis of maternal-fetal transmission of Tc and provide a justification for the investment in the development of vaccines against congenital CD.

Redox Balance Keepers and Possible Cell Functions Managed by Redox Homeostasis in Trypanosoma cruzi

The toxicity of oxygen and nitrogen reactive species appears to be merely the tip of the iceberg in the world of redox homeostasis. Now, oxidative stress can be seen as a two-sided process; at high concentrations, it causes damage to biomolecules, and thus, trypanosomes have evolved a strong antioxidant defense system to cope with these stressors. At low concentrations, oxidants are essential for cell signaling, and in fact, the oxidants/antioxidants balance may be able to trigger different cell fates. In this comprehensive review, we discuss the current knowledge of the oxidant environment experienced by T. cruzi along the different phases of its life cycle, and the molecular tools exploited by this pathogen to deal with oxidative stress, for better or worse. Further, we discuss the possible redox-regulated processes that could be governed by this oxidative context. Most of the current research has addressed the importance of the trypanosomes' antioxidant network based on its detox activity of harmful species; however, new efforts are necessary to highlight other functions of this network and the mechanisms underlying the fine regulation of the defense machinery, as this represents a master key to hinder crucial pathogen functions. Understanding the relevance of this balance keeper program in parasite biology will give us new perspectives to delineate improved treatment strategies.

Immunity and vaccine development efforts against Trypanosoma cruzi

Trypanosoma cruzi (T. cruzi) is the causative agent for Chagas disease (CD). There is a critical lack of methods for prevention of infection or treatment of acute infection and chronic disease. Studies in experimental models have suggested that the protective immunity against T. cruzi infection requires the elicitation of Th1 cytokines, lytic antibodies and the concerted activities of macrophages, T helper cells, and cytotoxic T lymphocytes (CTLs). In this review, we summarize the research efforts in vaccine development to date and the challenges faced in achieving an efficient prophylactic or therapeutic vaccine against human CD.

Metabolic programming of macrophage functions and pathogens control

Macrophages (Mφ) are central players in mediating proinflammatory and immunomodulatory functions. Unchecked Mφ activities contribute to pathology across many diseases, including those caused by infectious pathogens and metabolic disorders. A fine balance of Mφ responses is crucial, which may be achieved by enforcing appropriate bioenergetics pathways. Metabolism serves as the provider of energy, substrates, and byproducts that support differential Mφ characteristics. The metabolic properties that control the polarization and response of Mφ remain to be fully uncovered for use in managing infectious diseases. Here, we review the various metabolic states in Mφ and how they influence the cell function.

Trypanothione synthetase confers growth, survival advantage and resistance to anti-protozoal drugs in Trypanosoma cruzi

BACKGROUND

Chagas cardiomyopathy, caused by Trypanosoma cruzi infection, continues to be a neglected illness, and has a major impact on global health. The parasite undergoes several stages of morphological and biochemical changes during its life cycle, and utilizes an elaborated antioxidant network to overcome the oxidants barrier and establish infection in vector and mammalian hosts. Trypanothione synthetase (TryS) catalyzes the biosynthesis of glutathione-spermidine adduct trypanothione (T(SH)₂) that is the principal intracellular thiol-redox metabolite in trypanosomatids.

METHODS AND RESULTS

We utilized genetic overexpression (TryS^hi) and pharmacological inhibition approaches to examine the role of TryS in T. cruzi proliferation, tolerance to oxidative stress and resistance to anti-protozoal drugs. Our data showed the expression and activity of TryS was increased in all morphological stages of TryS^hi (vs. control) parasites. In comparison to controls, the TryS^hi epimastigotes (insect stage) recorded shorter doubling time, and both epimastigotes and infective trypomastigotes of TryS^hi exhibited 36-71% higher resistance to H₂O₂ (50-1000 μM) and heavy metal (1-500 μM) toxicity. Treatment with TryS inhibitors (5-30 μM) abolished the proliferation and survival advantages against H₂O₂ pressure in a dose-dependent manner in both TryS^hi and control parasites. Further, epimastigote and trypomastigote forms of TryS^hi (vs. control) T. cruzi tolerated higher doses of benznidazole and nifurtimox, the drugs currently administered for acute Chagas disease treatment.

CONCLUSIONS

TryS is essential for proliferation and survival of T. cruzi under normal and oxidant stress conditions, and provides an advantage to the parasite to develop resistance against currently used anti-trypanosomal drugs. TryS indispensability has been chemically validated with inhibitors that may be useful for drug combination therapy against Chagas disease.

Pathology and Pathogenesis of Chagas Heart Disease

Chagas heart disease is an inflammatory cardiomyopathy that develops in approximately one-third of people infected with the protozoan parasite Trypanosoma cruzi. One way T. cruzi is transmitted to people is through contact with infected kissing bugs, which are found in much of the Western Hemisphere, including in vast areas of the United States. The epidemiology of T. cruzi and Chagas heart disease and the varied mechanisms leading to myocyte destruction, mononuclear cell infiltration, fibrosis, and edema in the heart have been extensively studied by hundreds of scientists for more than 100 years. Despite this wealth of knowledge, it is still impossible to predict what will happen in an individual infected with T. cruzi because of the tremendous variability in clonal parasite virulence and human susceptibility to infection and the lack of definitive molecular predictors of outcome from either side of the host-parasite equation. Further, while several distinct mechanisms of pathogenesis have been studied in isolation, it is certain that multiple coincident mechanisms combine to determine the ultimate outcome. For these reasons, Chagas disease is best considered a collection of related but distinct illnesses. This review highlights the pathology and pathogenesis of the most common adverse sequela of T. cruzi infection-Chagas heart disease-and concludes with a discussion of key unanswered questions and a view to the future.

Proinflammatory Effects of Respiratory Syncytial Virus-Induced Epithelial HMGB1 on Human Innate Immune Cell Activation

High mobility group box 1 (HMGB1) is a multifunctional nuclear protein that translocates to the cytoplasm and is subsequently released to the extracellular space during infection and injury. Once released, it acts as a damage-associated molecular pattern and regulates immune and inflammatory responses. Respiratory syncytial virus (RSV) is a major cause of acute lower respiratory tract infections in infants and elderly, for which no effective treatment or vaccine is currently available. This study investigated the effects of HMGB1 on cytokine secretion, as well as the involvement of NF-κB and TLR4 pathways in RSV-induced HMGB1 release in human airway epithelial cells (AECs) and its proinflammatory effects on several human primary immune cells. Purified HMGB1 was incubated with AECs (A549 and small alveolar epithelial cells) and various immune cells and measured the release of proinflammatory mediators and the activation of NF-κB and P38 MAPK. HMGB1 treatment significantly increased the phosphorylation of NF-κB and P38 MAPK but did not induce the release of cytokines/chemokines from AECs. However, addition of HMGB1 to immune cells did significantly induce the release of cytokines/chemokines and activated the NF-κB and P38 MAPK pathways. We found that activation of NF-κB accounted for RSV-induced HMGB1 secretion in AECs in a TLR4-dependent manner. These results indicated that HMGB1 secreted from AECs can facilitate the secretion of proinflammatory mediators from immune cells in a paracrine mechanism, thus promoting the inflammatory response that contributes to RSV pathogenesis. Therefore, blocking the proinflammatory function of HMGB1 may be an effective approach for developing novel therapeutics.

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.

Abstract 399: Inhibition of NFE2L2-ARE Pathway by mtROS Contributes to Development of Cardiomyopathy and Left Ventricular Dysfunction in Chagas Disease

Aims: We investigated the effects of mitochondrial reactive oxygen species (mtROS) on nuclear factor (erythroid 2)-like 2 (NFE2L2) transcription factor activity during Trypanosoma cruzi (Tc) infection and determined whether enhancing the mtROS scavenging capacity preserved the heart function in Chagas disease.

Results: C57BL/6 wild type (WT, female) mice infected with Tc exhibited myocardial loss of mitochondrial membrane potential, complex II (CII)-driven coupled respiration, and ninefold increase in mtROS production. In vitro and in vivo studies showed that Tc infection resulted in an ROS-dependent decline in the expression, nuclear translocation, antioxidant response element (ARE) binding, and activity of NFE2L2, and 35-99% decline in antioxidants’ (gamma-glutamyl cysteine synthase [γGCS], heme oxygenase-1 [HO1], glutamate-cysteine ligase modifier subunit [GCLM], thioredoxin (Trx), glutathione S transferase [GST], and NAD(P)H dehydrogenase, quinone 1 [NQO1]) expression. An increase in myocardial and mitochondrial oxidative adducts, myocardial interventricular septum thickness, and left ventricle (LV) mass, a decline in LV posterior wall thickness, and disproportionate synthesis of collagens (COLI/COLIII), αSMA, and SM22α were noted in WT.Tc mice. Overexpression of manganese superoxide dismutase (MnSOD) in cultured cells (HeLa or cardiomyocytes) and MnSODtg mice preserved the NFE2L2 transcriptional activity and antioxidant/oxidant balance, and cardiac oxidative and fibrotic pathology were significantly decreased in MnSODtg.Tc mice. Importantly, echocardiography finding of a decline in LV systolic (stroke volume, cardiac output, ejection fraction) and diastolic (early/late peak filling ratio, myocardial performance index) function in WT.Tc mice was abolished in MnSODtg.Tc mice.

Innovation and Conclusion: The mtROS inhibition of NFE2L2/ARE pathway constitutes a key mechanism in signaling the fibrotic gene expression and evolution of chronic cardiomyopathy. Preserving the NFE2L2 activity arrested the mitochondrial and cardiac oxidative stress, cardiac fibrosis, and heart failure in Chagas disease.

Pathogenesis of Chronic Chagas Disease: Macrophages, Mitochondria, and Oxidative Stress

PURPOSE OF REVIEW

Trypanosoma cruzi is the causative agent of Chagas disease. Decades after initial infection, ~30% of individuals can develop chronic chagasic cardiomyopathy. There are several proposed mechanisms for pathogenesis of Chagas disease, including parasite persistence, immune responses against parasite or self that continue in the heart, vascular compromise, and involvement of autonomous and central nervous system. Herein, we will focus on the significance of macrophages, mitochondrial dysfunction, and oxidative stress in progression of chagasic cardiomyopathy.

RECENT FINDINGS

The current literature suggests that T. cruzi prevents cytotoxic activities of the innate immune cells and persists in the host, contributing to mitochondrial oxidative stress. We discuss how the neoantigens generated due to cellular oxidative damage contribute to chronic inflammatory stress in chagasic disease.

SUMMARY

We propose that metabolic regulators, PARP-1/SIRT1, determine the disease outcome by modulating the mitochondrial and macrophage stress and antioxidant/oxidant imbalance, and offer a potential new therapy against chronic Chagas disease.

Quantitative and histological assessment of maternal-fetal transmission of Trypanosoma cruzi in guinea pigs: An experimental model of congenital Chagas disease

OBJECTIVE

We evaluated the effect of Trypanosoma cruzi infection on fertility, gestation outcome, and maternal-fetal transmission in guinea pigs (Cavia porcellus).

METHODS

Animals were infected with T. cruzi H4 strain (TcI lineage) before gestation (IBG) or during gestation (IDG). Tissue and sera samples of dams and fetuses were obtained near parturition.

RESULTS

All IBG and IDG dams were seropositive by two tests, and exhibited blood parasite load of 1.62±2.2 and 50.1±62 parasites/μl, respectively, by quantitative PCR. Histological evaluation showed muscle fiber degeneration and cellular necrosis in all infected dams. Parasite nests were not detected in infected dams by histology. However, qPCR analysis detected parasites-eq/g heart tissue of 153±104.7 and 169.3±129.4 in IBG and IDG dams, respectively. All fetuses of infected dams were positive for anti-parasite IgG antibodies and tissue parasites by qPCR, but presented a low level of tissue inflammatory infiltrate. Fetuses of IDG (vs. IBG) dams exhibited higher degree of muscle fiber degeneration and cellular necrosis in the heart and skeletal tissues. The placental tissue exhibited no inflammatory lesions and amastigote nests, yet parasites-eq/g of 381.2±34.3 and 79.2±84.9 were detected in IDG and IBG placentas, respectively. Fetal development was compromised, and evidenced by a decline in weight, crow-rump length, and abdominal width in both groups.

CONCLUSIONS

T. cruzi TcI has a high capacity of congenital transmission even when it was inoculated at a very low dose before or during gestation. Tissue lesions, parasite load, and fetal under development provide evidence for high virulence of the parasite during pregnancy. Despite finding of high parasite burden by qPCR, placentas were protected from cellular damage. Our studies offer an experimental model to study the efficacy of vaccines and drugs against congenital transmission of T. cruzi. These results also call for T. cruzi screening in pregnant women and adequate follow up of the newborns in endemic areas.

Differential inflammasome activation signatures following intracellular infection of human macrophages with Mycobacterium bovis BCG or Trypanosoma cruzi

Pathogens frequently exploit or evade inflammasome activation in order to survive and proliferate. Alternatively, inadequate inflammasome activation by attenuated microorganisms or adjuvanted subunit vaccines may contribute to poor longevity of protection. To further understand these pathways, we determined the differential inflammasome transcriptome of human THP monocyte-derived macrophages in response to Mycobacterium bovis BCG, as compared to LPS or Trypanosoma cruzi. The results identify the highly specific innate recognition programs associated with inflammasome activation by human macrophages exposed to these microbial stimuli. BCG, T. cruzi, and LPS strongly induced expression of both unique and overlapping genes downstream of TLR signaling pathways including cytokines and chemokines that mediate inflammation and regulate cell death pathways. Compared to LPS, BCG failed to directly activate anti-apoptotic molecules and multiple NLR and inflammasome complex components including caspase-1, and actively repressed important signaling intermediates in AP-1 and NFκB transcription factor pathways. Both BCG and T. cruzi repressed expression of TXNIP, an anti-oxidant inhibitor that recruits caspase-1 to the NLRP3 inflammasome, while T. cruzi infection uniquely failed to activate TNF-α. These results identify unique pathogen specific strategies to activate inflammation and modulate cell death that may drive inflammatory outcomes and suggest avenues of investigation to optimize host immunity.

Dysregulation of RBFOX2 Is an Early Event in Cardiac Pathogenesis of Diabetes

Alternative splicing (AS) defects that adversely affect gene expression and function have been identified in diabetic hearts; however, the mechanisms responsible are largely unknown. Here, we show that the RNA-binding protein RBFOX2 contributes to transcriptome changes under diabetic conditions. RBFOX2 controls AS of genes with important roles in heart function relevant to diabetic cardiomyopathy. RBFOX2 protein levels are elevated in diabetic hearts despite low RBFOX2 AS activity. A dominant-negative (DN) isoform of RBFOX2 that blocks RBFOX2-mediated AS is generated in diabetic hearts. DN RBFOX2 interacts with wild-type (WT) RBFOX2, and ectopic expression of DN RBFOX2 inhibits AS of RBFOX2 targets. Notably, DN RBFOX2 expression is specific to diabetes and occurs at early stages before cardiomyopathy symptoms appear. Importantly, DN RBFOX2 expression impairs intracellular calcium release in cardiomyocytes. Our results demonstrate that RBFOX2 dysregulation by DN RBFOX2 is an early pathogenic event in diabetic hearts.

Abstract 83: Modulation of Macrophage Function via Metabolism by Trypanosoma cruzi

Chagas heart disease is an inflammatory cardiomyopathy which presents with mononuclear infiltrates in the interstitium and myocardial fibrosis in the chronic phase. Incomplete clearance by macrophages of the etiologic agent, Trypanosoma cruzi , is a significant cause of chronic disease development in approximately 30% of those serologically positive for the blood-borne parasite. The differential metabolic status, anaerobic glycolysis and mitochondria-dependent oxidative phosphorylation, are respectively associated with pro-inflammatory (M1) and anti-inflammatory (M2) functional activation of macrophages. Reactive oxygen species (ROS) have been shown to be an intracellular signal for glycolysis while peroxisome proliferator-activated receptors (PPARs) that enhance fatty acid oxidation provide transcription control of macrophage functional state. In our studies using diverse T. cruzi isolates, we showed that SylvioX10 (virulent), but not TCC (non-virulent), isolates are able to differentially control extracellular and intracellular ROS levels in macrophages. We found in macrophages infected with SylvioX10, the nuclear expression of PPAR-α was increased by 18 hours post-infection, and mitochondrial metabolic activity was similar to that of not-infected and M2 controls; which indicates anti-inflammatory function of macrophages, and therefore prohibiting T. cruzi clearance. In our ongoing studies, we are examining the impact of PPAR-α inhibitors in modulating the metabolic gene expression profile, functional phenotype and parasite survival in macrophages. Our data will provide the first indication that host macrophages have deficient pro-inflammatory capacity due to sub-optimal glucose oxidation, and enhancing the metabolism that supports T. cruzi clearance will provide a valuable basis for a strategy to arrest Chagas disease progression.

Abstract 82: Mnsodtg Mice Exhibit Improved Heart and Mitochondrial Function During Chronic Chagas Disease

Background: We observed that mitochondrial reactive oxygen species (mtROS) plays very important roles in the pregression of chagesic disease (CD). In this study, we utilized genetically-modified mice to scavenge mtROS to investigate the impact of improved ROS scavenging capacity on heart function in CD.

Methods and Results: C57BL/6 mice (wild-type, MnSODtg, MnSOD+/-) were infected with Trypanosoma cruzi(Tc). Chronically infected mice (≥120dpi) exhibited a substantial decrease in heart tissue MnSOD gene expression, protein level, enzyme activity and antioxidant level; decrease of heart dysfunction via lower of SV, CO, EF, FS and LVPW,s, and increase of ESV/EDS and LVID;s; enhancement of hypertrophy by increase of IVS, LV mass and areas duo to augmentation of collagen expressions. One of our novel observations was that sarco/endoplasmic reticulum Ca2+-ATPase (SERCA2) lost its role of maintenance of low cytoplasm free calcium and mediated calcium uptake to intracellular store in Tc-induced chronic chagasic disease. Studies of fresh heart slices using O2K confirmed that Tc diminished heart mitochondrial function like decrease of oxygen flux and respiratory control ratio (RCR), which were caused by enhancements of ROS. Myocardial mitochondrial damage was pronounced and associated with a >x% decline in mitochondrial oxygen flux in chronically infected wild-type and MnSOD transgenic mice. Imaging of intact heart for cardiomyocytes and collagen by the nonlinear optical microscopy techniques showed significant increase in collagen (>x0-fold) in chronically infected wild-type mice; while MnSODtg mice exhibited a basal increase in collagen that did not change during chronic phase. Chronically infected MnSODtg mice exhibited a marginal decline in Tc-induced heart function, heart hypertrophy, mitochondrial dysfunction

Conclusions: Overexpression of MnSOD inhibited Tc-induced oxidative damage od heart tissue. , suggesting that enhancing the mitochondrial ROS scavenging capacity was beneficial in controlling the inflammatory and oxidative pathology, and cardiac remodeling responses that are hallmarks of chronic Chagas disease.

A Two-Component DNA-Prime/Protein-Boost Vaccination Strategy for Eliciting Long-Term, Protective T Cell Immunity against Trypanosoma cruzi

In this study, we evaluated the long-term efficacy of a two-component subunit vaccine against Trypanosoma cruzi infection. C57BL/6 mice were immunized with TcG2/TcG4 vaccine delivered by a DNA-prime/Protein-boost (D/P) approach and challenged with T. cruzi at 120 or 180 days post-vaccination (dpv). We examined whether vaccine-primed T cell immunity was capable of rapid expansion and intercepting the infecting T. cruzi. Our data showed that D/P vaccine elicited CD4⁺ (30-38%) and CD8⁺ (22-42%) T cells maintained an effector phenotype up to 180 dpv, and were capable of responding to antigenic stimulus or challenge infection by a rapid expansion (CD8>CD4) with type 1 cytokine (IFNγ⁺ and TFNα⁺) production and cytolytic T lymphocyte (CTL) activity. Subsequently, challenge infection at 120 or 180 dpv, resulted in 2-3-fold lower parasite burden in vaccinated mice than was noted in unvaccinated/infected mice. Co-delivery of IL-12- and GMCSF-encoding expression plasmids provided no significant benefits in enhancing the anti-parasite efficacy of the vaccine-induced T cell immunity. Booster immunization (bi) with recombinant TcG2/TcG4 proteins 3-months after primary vaccine enhanced the protective efficacy, evidenced by an enhanced expansion (1.2-2.8-fold increase) of parasite-specific, type 1 CD4⁺ and CD8⁺ T cells and a potent CTL response capable of providing significantly improved (3-4.5-fold) control of infecting T. cruzi. Further, CD8⁺T cells in vaccinated/bi mice were predominantly of central memory phenotype, and capable of responding to challenge infection 4-6-months post bi by a rapid expansion to a poly-functional effector phenotype, and providing a 1.5-2.3-fold reduction in tissue parasite replication. We conclude that the TcG2/TcG4 D/P vaccine provided long-term anti-T. cruzi T cell immunity, and bi would be an effective strategy to maintain or enhance the vaccine-induced protective immunity against T. cruzi infection and Chagas disease.

Chagas disease, caused by Trypanosoma cruzi infection, represents the third greatest tropical disease burden in the world. No vaccine or suitable treatment is available for control of this infection. Based upon several studies we have conducted, we believe that TcG2 and TcG4 candidate antigens that are highly conserved in T. cruzi, expressed in clinically relevant forms of the parasite, and recognized by both B and T cell responses in multiple hosts, are an excellent choice for subunit vaccine development. In this study, we demonstrate that the delivery of TcG2 and TcG4 as a DNA-prime/protein-boost vaccine provided long-term protection from challenge infection, and this protection was associated with elicitation of long-lived CD8⁺ effector T cells. The longevity and efficacy of vaccine could be enhanced by booster immunization. We believe that this is the first report demonstrating a) a subunit vaccine can be useful in achieving long-term protection against T. cruzi infection and Chagas disease, and b) the effector T cells can be long-lived and play a role in vaccine elicited protection from parasitic infection.

Immune protection against Trypanosoma cruzi induced by TcVac4 in a canine model

Chagas disease, caused by Trypanosoma cruzi, is endemic in southern parts of the American continent. Herein, we have tested the protective efficacy of a DNA-prime/T. rangeli-boost (TcVac4) vaccine in a dog (Canis familiaris) model. Dogs were immunized with two-doses of DNA vaccine (pcDNA3.1 encoding TcG1, TcG2, and TcG4 antigens plus IL-12- and GM-CSF-encoding plasmids) followed by two doses of glutaraldehyde-inactivated T. rangeli epimastigotes (TrIE); and challenged with highly pathogenic T. cruzi (SylvioX10/4) isolate. Dogs given TrIE or empty pcDNA3.1 were used as controls. We monitored post-vaccination and post-challenge infection antibody response by an ELISA, parasitemia by blood analysis and xenodiagnosis, and heart function by electrocardiography. Post-mortem anatomic and pathologic evaluation of the heart was conducted. TcVac4 induced a strong IgG response (IgG2>IgG1) that was significantly expanded post-infection, and moved to a nearly balanced IgG2/IgG1 response in chronic phase. In comparison, dogs given TrIE or empty plasmid DNA only developed high IgG titers with IgG2 predominance in response to T. cruzi infection. Blood parasitemia, tissue parasite foci, parasite transmission to triatomines, electrocardiographic abnormalities were significantly lower in TcVac4-vaccinated dogs than was observed in dogs given TrIE or empty plasmid DNA only. Macroscopic and microscopic alterations, the hallmarks of chronic Chagas disease, were significantly decreased in the myocardium of TcVac4-vaccinated dogs. We conclude that TcVac4 induced immunity was beneficial in providing resistance to T. cruzi infection, evidenced by control of chronic pathology of the heart and preservation of cardiac function in dogs. Additionally, TcVac4 vaccination decreased the transmission of parasites from vaccinated/infected animals to triatomines.

Current understanding of immunity to Trypanosoma cruzi infection and pathogenesis of Chagas disease

Chagas disease caused by Trypanosoma cruzi remains an important neglected tropical disease and a cause of significant morbidity and mortality. No longer confined to endemic areas of Latin America, it is now found in non-endemic areas due to immigration. The parasite may persist in any tissue, but in recent years, there has been increased recognition of adipose tissue both as an early target of infection and a reservoir of chronic infection. The major complications of this disease are cardiomyopathy and megasyndromes involving the gastrointestinal tract. The pathogenesis of Chagas disease is complex and multifactorial involving many interactive pathways. The significance of innate immunity, including the contributions of cytokines, chemokines, reactive oxygen species, and oxidative stress, has been emphasized. The role of the components of the eicosanoid pathway such as thromboxane A(2) and the lipoxins has been demonstrated to have profound effects as both pro- and anti-inflammatory factors. Additionally, we discuss the vasoconstrictive actions of thromboxane A(2) and endothelin-1 in Chagas disease. Human immunity to T. cruzi infection and its role in pathogen control and disease progression have not been fully investigated. However, recently, it was demonstrated that a reduction in the anti-inflammatory cytokine IL-10 was associated with clinically significant chronic chagasic cardiomyopathy.

Mechanisms of Trypanosoma cruzi persistence in Chagas disease

Trypanosoma cruzi infection leads to development of chronic Chagas disease. In this article, we provide an update on the current knowledge of the mechanisms employed by the parasite to gain entry into the host cells and establish persistent infection despite activation of a potent immune response by the host. Recent studies point to a number of T. cruzi molecules that interact with host cell receptors to promote parasite invasion of the diverse host cells. T. cruzi expresses an antioxidant system and thromboxane A(2) to evade phagosomal oxidative assault and suppress the host's ability to clear parasites. Additional studies suggest that besides cardiac and smooth muscle cells that are the major target of T. cruzi infection, adipocytes and adipose tissue serve as reservoirs from where T. cruzi can recrudesce and cause disease decades later. Further, T. cruzi employs at least four strategies to maintain a symbiotic-like relationship with the host, and ensure consistent supply of nutrients for its own survival and long-term persistence. Ongoing and future research will continue to help refining the models of T. cruzi invasion and persistence in diverse tissues and organs in the host.