Chronic Trypanosoma cruzi infection potentiates adipose tissue macrophage polarization toward an anti-inflammatory M2 phenotype and contributes to diabetes progression in a diet-induced obesity model

Targeting Macrophage Polarization in Infectious Diseases: M1/M2 Functional Profiles, Immune Signaling and Microbial Virulence Factors

INTRODUCTION

An event of increasing interest during host-pathogen interactions is the polarization of patrolling/naive monocytes (MOs) into macrophage subsets (MФs). Therapeutic strategies aimed at modulating this event are under investigation.

METHODS

This review focuses on the mechanisms of induction/development and profile of MФs polarized toward classically proinflammatory (M1) or alternatively anti-inflammatory (M2) phenotypes in response to bacteria, fungi, parasites, and viruses.

RESULTS AND DISCUSSION

It highlights nuclear, cytoplasmic, and cell surface receptors (pattern recognition receptors/PPRs), microenvironmental mediators, and immune signaling. MФs polarize into phenotypes: M1 MФs, activated by IFN-γ, pathogen-associated molecular patterns (PAMPs, e.g. lipopolysaccharide) and membrane-bound PPRs ligands (TLRs/CLRs ligands); or M2 MФs, induced by interleukins (ILs-4, -10 and -13), antigen-antibody complexes, and helminth PAMPs. Polarization toward M1 and M2 profiles evolve in a pathogen-specific manner, with or without canonicity, and can vary widely. Ultimately, this can result in varying degrees of host protection or more severe disease outcome. On the one hand, the host is driving effective MФs polarization (M1 or M2); but on the other hand, microorganisms may skew the polarization through virulence factors to increase pathogenicity. Cellular/genomic reprogramming also ensures plasticity of M1/M2 phenotypes. Because modulation of polarization can occur at multiple points, new insights and emerging perspectives may have clinical implications during the inflammation-to-resolution transition; translated into practical applications as for therapeutic/vaccine design target to boost microbicidal response (M1, e.g. triggering oxidative burst) with specifics PAMPs/IFN-γ or promote tissue repair (M2, increasing arginase activity) via immunotherapy.

Interaction between peripheral blood mononuclear cells and Trypanosoma cruzi-infected adipocytes: implications for treatment failure and induction of immunomodulatory mechanisms in adipose tissue

Background/Introduction

Adipose tissue (AT) has been highlighted as a promising reservoir of infection for viruses, bacteria and parasites. Among them is Trypanosoma cruzi, which causes Chagas disease. The recommended treatment for the disease in Brazil is Benznidazole (BZ). However, its efficacy may vary according to the stage of the disease, geographical origin, age, immune background of the host and sensitivity of the strains to the drug. In this context, AT may act as an ally for the parasite survival and persistence in the host and a barrier for BZ action. Therefore, we investigated the immunomodulation of T. cruzi-infected human AT in the presence of peripheral blood mononuclear cells (PBMC) where BZ treatment was added.

Methods

We performed indirect cultivation between T. cruzi-infected adipocytes, PBMC and the addition of BZ. After 72h of treatment, the supernatant was collected for cytokine, chemokine and adipokine assay. Infected adipocytes were removed to quantify T. cruzi DNA, and PBMC were removed for immunophenotyping.

Results

Our findings showed elevated secretion of interleukin (IL)-6, IL-2 and monocyte chemoattractant protein-1 (MCP-1/CCL2) in the AT+PBMC condition compared to the other controls. In contrast, there was a decrease in tumor necrosis factor (TNF) and IL-8/CXCL-8 in the groups with AT. We also found high adipsin secretion in PBMC+AT+T compared to the treated condition (PBMC+AT+T+BZ). Likewise, the expression of CD80+ and HLA-DR+ in CD14+ cells decreased in the presence of T. cruzi.

Discussion

Thus, our findings indicate that AT promotes up-regulation of inflammatory products such as IL-6, IL-2, and MCP-1/CCL2. However, adipogenic inducers may have triggered the downregulation of TNF and IL-8/CXCL8 through the peroxisome proliferator agonist gamma (PPAR-g) or receptor expression. On the other hand, the administration of BZ only managed to reduce inflammation in the microenvironment by decreasing adipsin in the infected culture conditions. Therefore, given the findings, we can see that AT is an ally of the parasite in evading the host's immune response and the pharmacological action of BZ.

Effect of macrophage polarization on parasitic protection against type 1 diabetes mellitus

Type 1 diabetes mellitus is a chronic disease caused by the destruction of pancreatic beta cells. Based on the hygiene hypothesis, a growing body of evidence suggests a negative association between parasitic infections and diabetes in humans and animal models. The mechanism of parasite-mediated prevention of type 1 diabetes mellitus may be related to the adaptive and innate immune systems. Macrophage polarization is a new paradigm for the treatment of type 1 diabetes mellitus, and different host macrophage subsets play various roles during parasite infection. Proinflammatory cytokines are released by M1 macrophages, which are important in the development of type 1 diabetes mellitus. Parasite-activated M2 macrophages prevent the development of type 1 diabetes mellitus and can influence the development of adaptive immune responses through several mechanisms, including Th2 cells and regulatory T cells. Here, we review the role and mechanism of macrophage polarization in parasitic protection against type 1 diabetes mellitus.

Cafeteria diet-induced obesity remodels immune response in acute Trypanosoma cruzi infection

BACKGROUND

Obesity is a global problem associated with several conditions, including hypertension, diabetes, arthritis and cardiovascular diseases. With the increase in the prevalence of obesity in recent years, mostly in developing countries, it is important to study its impact on various diseases, including infectious illnesses, such as Chagas disease, caused by the protozoan Trypanosoma cruzi. Considering that a diet rich in salt, sugar, and fat is associated with obesity, this study aimed to evaluate the influence of cafeteria diet (CAF)-induced obesity on immune responses in T. cruzi-infected rats.

METHODS

Male Wistar Hannover rats were provided with water and food ad libitum (chow group). The CAF-fed groups received a normal rodent diet or CAF. The animals were intraperitoneally infected with 105 trypomastigote forms of the Y strain of T. cruzi present in the whole blood from a previously infected mouse.

RESULTS

CAF-fed rats showed a significant increase in visceral adipose tissue weight compared to chow-fed rats. A significant reduction in CD3+ CD4+ helper splenic T cells was observed in obese-infected rats compared to non-obese-infected rats, as well as CD11b and macrophages. In addition, macrophages from obese animals displayed reduced RT1b levels compared to those from control animals. Moreover, INF-γ, an important factor in macrophage activation, was reduced in obese-infected rats compared with their counterparts.

CONCLUSIONS

These results indicate that a CAF can impair the cell-mediated immune response against T. cruzi.

Benznidazole treatment decreases IL-6 levels in Trypanosoma cruzi-infected human adipocytes differentiated from adipose tissue-derived stem cells

BACKGROUND

Trypanosoma cruzi, which causes Chagas disease (CD), is a versatile haemoparasite that uses several strategies to evade the host's immune response, including adipose tissue (AT), used as a reservoir of infection. As it is an effective barrier to parasite evasion, the effectiveness of the drug recommended for treating CD, Benznidazole (BZ), may be questionable.

OBJECTIVE

To this end, we evaluated the parasite load and immunomodulation caused by BZ treatment in the culture of adipocytes differentiated from human adipose tissue-derived stem cells (ADSC) infected with T. cruzi.

METHODS

The ADSC were subjected to adipogenic differentiation. We then carried out four cultures in which we infected the differentiated AT with trypomastigote forms of the Y strain of T. cruzi and treated them with BZ. After the incubation, the infected AT was subjected to quantitative polymerase chain reaction (qPCR) to quantify the parasite load and transmission electron microscopy (TEM) to verify the infection. The supernatant was collected to measure cytokines, chemokines, and adipokines.

FINDINGS

We found elevated secretion of IL-6, CXCL-10/IP-10, CCL2/MCP-1, CCL5/RANTES, and leptin in infected fat cells. However, treatment with BZ promoted a decrease in IL-6.

MAIN CONCLUSION

Therefore, we believe that BZ has a beneficial role as it reduces inflammation in infected fat cells.

Comorbidities involving parasitic diseases: A look at the benefits and complications

Parasitic infections acquired by the population cause substantial morbidity worldwide, with individuals from developing countries being most affected. Some parasites remain in the host for long periods, settling in different organs, manipulating the flow of nutrients and metabolites, and influencing the immune response, favoring their adaptation. The host attempts to counteract the metabolic and immunological alterations and the possible damage caused by infection. These metabolic and immunological changes experienced by the host can influence the progression of other existing morbidities or those that will be acquired in the future. Cancer and metabolic diseases are also frequent causes of morbidity in the world population. The large numbers of individuals affected by cancer and metabolic diseases and the high prevalence of morbidity caused by parasitic diseases favor the development of comorbidity involving these pathologies. This review provides an overview of major advances in research on cancer and metabolic diseases associated with parasitic infections. Information about hosts and parasites such as alterations of the immune response, metabolism and adaptation mechanisms of the parasites, and parasitic molecules with therapeutic potential is provided, as well as the beneficial results or complications related to the comorbidities discussed herein. We emphasize the need to conduct additional studies addressing comorbidities associated with parasitic infections to improve the understanding of the impact of this association on the progression of morbidities, as well as the possibility of the therapeutic use of and therapeutic approaches involving parasites.

Immune and non-immune functions of adipose tissue leukocytes

Adipose tissue is a complex dynamic organ with whole-body immunometabolic influence. Much of the work into understanding the role of immune cells in adipose tissue has been in the context of obesity. These investigations have also uncovered a range of typical (immune) and non-typical functions exerted by adipose tissue leukocytes. Here we provide an overview of the adipose tissue immune system, including its role as an immune reservoir in the whole-body response to infection and as a site of parasitic and viral infections. We also describe the functional roles of specialized immunological structures found within adipose tissue. However, our main focus is on the recently discovered 'non-immune' functions of adipose tissue immune cells, which include the regulation of adipocyte homeostasis, as well as responses to changing nutrient status and body temperature. In doing so, we outline the therapeutic potential of the adipose tissue immune system in health and disease.

Helminth and Host Crosstalk: New Insight Into Treatment of Obesity and Its Associated Metabolic Syndromes

Obesity and its associated Metabolic Syndromes (Mets) represent a global epidemic health problem. Metabolic inflammation, lipid accumulation and insulin resistance contribute to the progression of these diseases, thereby becoming targets for drug development. Epidemiological data have showed that the rate of helminth infection negatively correlates with the incidence of obesity and Mets. Correspondingly, numerous animal experiments and a few of clinic trials in human demonstrate that helminth infection or its derived molecules can mitigate obesity and Mets via induction of macrophage M2 polarization, inhibition of adipogenesis, promotion of fat browning, and improvement of glucose tolerance, insulin resistance and metabolic inflammation. Interestingly, sporadic studies also uncover that several helminth infections can reshape gut microbiota of hosts, which is intimately implicated in the pathogenesis of obesity and Mets. Overall, these findings indicate that the crosstalk between helminth and hosts may be a novel direction for obesity and Mets therapy. The present article reviews the molecular mechanism of how helminth masters immunity and metabolism in obesity.

Trypanosoma brucei triggers a broad immune response in the adipose tissue

Adipose tissue is one of the major reservoirs of Trypanosoma brucei parasites, the causative agent of sleeping sickness, a fatal disease in humans. In mice, the gonadal adipose tissue (AT) typically harbors 2–5 million parasites, while most solid organs show 10 to 100-fold fewer parasites. In this study, we tested whether the AT environment responds immunologically to the presence of the parasite. Transcriptome analysis of T. brucei infected adipose tissue revealed that most upregulated host genes are involved in inflammation and immune cell functions. Histochemistry and flow cytometry confirmed an increasingly higher number of infiltrated macrophages, neutrophils and CD4+ and CD8+ T lymphocytes upon infection. A large proportion of these lymphocytes effectively produce the type 1 effector cytokines, IFN-γ and TNF-α. Additionally, the adipose tissue showed accumulation of antigen-specific IgM and IgG antibodies as infection progressed. Mice lacking T and/or B cells (Rag2^-/-, Jht^-/-), or the signature cytokine (Ifng^-/-) displayed a higher parasite load both in circulation and in the AT, demonstrating the key role of the adaptive immune system in both compartments. Interestingly, infections of C3^-/- mice showed that while complement system is dispensable to control parasite load in the blood, it is necessary in the AT and other solid tissues. We conclude that T. brucei infection triggers a broad and robust immune response in the AT, which requires the complement system to locally reduce parasite burden.

African trypanosomiasis is a neglected disease with significant socio-economic burden in sub-Saharan Africa. The protozoan parasite Trypanosoma brucei, a causative agent of African trypanosomiasis, can be found in the blood and extra-vascular spaces of the infected host. For an unknown reason, T. brucei accumulates in adipose tissue (AT) in very high numbers. Here we used a multidisciplinary approach to assess whether an immune response was mounted in AT during a T. brucei infection. We found that as infection progresses, a broad variety of immune cells and antibodies accumulate in the AT. We also found that this broad immune response is partially able to control parasite numbers in the AT. Our study provides evidence that T. brucei parasites present in the AT are subjected to immune surveillance. The reason why T. brucei accumulates to such a high extent in AT remains to be elucidated.

Chagas disease is not associated with diabetes, metabolic syndrome, insulin resistance and beta cell dysfunction at baseline of Brazilian Longitudinal Study of Adult Health (ELSA-Brasil)

Chagas disease (ChD) affects millions of people worldwide, being endemic in Latin America and emerging in the United States and Europe. Classically described as targeting the heart and gastrointestinal tract, Trypanosoma cruzi parasitism leads to structural and pro-inflammatory changes in the adipose tissue and pancreas. The effects of these changes on insulin resistance (IR), beta cell dysfunction, diabetes mellitus (DM),and metabolic syndrome (MS) are unclear. We aim to evaluate the association of ChD with DM, IR, beta cell dysfunction and MS in the baseline of multi-centric cohort study 'Brazilian Longitudinal Study of Adult Health' (ELSA-Brasil). This cross-sectional analysis included 14,922 (98%) participants of ELSA-Brasil at baseline. To investigate the associations of ChD with DM, IR (assessed by HOMA-IR) and beta cell dysfunction (assessed by HOMA beta), and MS we fitted logistic regression models including socio-demographic and anthropometric variables, health-related conditions and laboratory results. ChD, defined by positive serology, was prevalent in 1.9% (n = 283) of the sample, 17.3% (n = 49) of whom had cardiomyopathy. DM prevalence was 17.25% (n = 2574) and was not different among those with and without ChD (20.5% vs 17.2%; p = 0.28). Fasting and 2 h-blood glucose after a 75 g anhydrous glucose were slightly higher among participants positive for ChD, when compared with those with negative serology (102 mg/dL versus 100 mg/dL, respectively; and 127 mg/dL versus 124 mg/dL, respectively), only in univariate analysis. There was no significant association between these variables and ChD after adjustments. In addition, there was no significant association between DM, IR, beta cell dysfunction or MS and ChD (without and with cardiomyopathy). Our results showed that ChD, regardless of the presence of cardiomyopathy, is not associated with DM, IR, beta cell dysfunction or MS. These findings suggest the parasitism of the adipose tissue and pancreas in Chagas disease do not translate into clinically relevant glucose abnormalities.

Infections at the nexus of metabolic-associated fatty liver disease

Metabolic-associated fatty liver disease (MAFLD) is a chronic liver disease that affects about a quarter of the world population. MAFLD encompasses different disease stadia ranging from isolated liver steatosis to non-alcoholic steatohepatitis (NASH), fibrosis, cirrhosis and hepatocellular carcinoma. Although MAFLD is considered as the hepatic manifestation of the metabolic syndrome, multiple concomitant disease-potentiating factors can accelerate disease progression. Among these risk factors are diet, lifestyle, genetic traits, intake of steatogenic drugs, male gender and particular infections. Although infections often outweigh the development of fatty liver disease, pre-existing MAFLD could be triggered to progress towards more severe disease stadia. These combined disease cases might be underreported because of the high prevalence of both MAFLD and infectious diseases that can promote or exacerbate fatty liver disease development. In this review, we portray the molecular and cellular mechanisms by which the most relevant viral, bacterial and parasitic infections influence the progression of fatty liver disease and steatohepatitis. We focus in particular on how infectious diseases, including coronavirus disease-19, hepatitis C, acquired immunodeficiency syndrome, peptic ulcer and periodontitis, exacerbate MAFLD. We specifically underscore the synergistic effects of these infections with other MAFLD-promoting factors.

Diet Rich in Lard Promotes a Metabolic Environment Favorable to Trypanosoma cruzi Growth

Background: Trypanosoma cruzi is a protozoan parasite that causes Chagas disease and affects 6-7 million people mainly in Latin America and worldwide. Here, we investigated the effects of hyperlipidic diets, mainly composed of olive oil or lard on experimental T. cruzi infection. C57BL/6 mice were fed two different dietary types in which the main sources of fatty acids were either monounsaturated (olive oil diet) or saturated (lard diet). Methods: After 60 days on the diet, mice were infected with 50 trypomastigote forms of T. cruzi Colombian strain. We evaluated the systemic and tissue parasitism, tissue inflammation, and the redox status of mice after 30 days of infection. Results: Lipid levels in the liver of mice fed with the lard diet increased compared with that of the mice fed with olive oil or normolipidic diets. The lard diet group presented with an increased parasitic load in the heart and adipose tissues following infection as well as an increased expression of Tlr2 and Tlr9 in the heart. However, no changes were seen in the survival rates across the dietary groups. Infected mice receiving all diets presented comparable levels of recruited inflammatory cells at 30 days post-infection but, at this time, we observed lard diet inducing an overproduction of CCL2 in the cardiac tissue and its inhibition in the adipose tissue. T. cruzi infection altered liver antioxidant levels in mice, with the lard diet group demonstrating decreased catalase (CAT) activity compared with that of other dietary groups. Conclusions: Our data demonstrated that T. cruzi growth is more favorable on tissue of mice subjected to the lard diet. Our findings supported our hypothesis of a relationship between the source of dietary lipids and parasite-induced immunopathology.

Association between Toxoplasma gondii infection and metabolic syndrome in obese adolescents: A possible immune-metabolic link

Background Toxoplasmosis as a global disease is considered as a triggering factor responsible for development of several clinical diseases. However, Toxoplasma gondii (T. gondii) is an understudied parasite of potential interest in obesity research. The current study aimed to explore the role of latent T. gondii infection in the pathogenesis of metabolic syndrome (MetS) in obese adolescents through studying the relationship between serum interferon-gamma [IFN-γ] and serum chemerin in context of MetS components. Methods Eighty-three obese adolescents were serologically screened for T. gondii-IgG antibodies and compared to 35 age-matched healthy T. gondii-seronegative controls. Participants were evaluated for anthropometric measurements, total-fat mass [FM], trunk-FM, serum lipid profile, IFN-γ, and chemerin levels. Homeostatic Model Assessment of insulin resistance (HOMA-IR) was calculated. Results The prevalence of MetS was significantly higher within obese T. gondii-seropositive group compared to obese T. gondii-seronegative group (P = 0.033). Seropositive obese MetS group displayed significantly higher trunk-FM, HOMA-IR, chemerin, and IFN-γ compared to seronegative obese MetS group. Serum chemerin and IFN-γ were strongly correlated (P < 0.001) and were positively correlated with BMI, WC, total-FM, trunk-FM, HOMA-IR, cholesterol, triglycerides and negatively correlated with HDLC. HOMA-IR was a common predictor for serum chemerin (P = 0.030) and IFN-γ (P < 0.001). Conclusions The study results suggest that T. gondii infection may exert an immune-metabolic effect that may have a potential role in the development of MetS among obese adolescents.

Brucella: Reservoirs and Niches in Animals and Humans

Brucella is an intracellular bacterium that causes abortion, reproduction failure in livestock and leads to a debilitating flu-like illness with serious chronic complications if untreated in humans. As a successful intracellular pathogen, Brucella has developed strategies to avoid recognition by the immune system of the host and promote its survival and replication. In vivo, Brucellae reside mostly within phagocytes and other cells including trophoblasts, where they establish a preferred replicative niche inside the endoplasmic reticulum. This process is central as it gives Brucella the ability to maintain replicating-surviving cycles for long periods of time, even at low bacterial numbers, in its cellular niches. In this review, we propose that Brucella takes advantage of the environment provided by the cellular niches in which it resides to generate reservoirs and disseminate to other organs. We will discuss how the favored cellular niches for Brucella infection in the host give rise to anatomical reservoirs that may lead to chronic infections or persistence in asymptomatic subjects, and which may be considered as a threat for further contamination. A special emphasis will be put on bone marrow, lymph nodes, reproductive and for the first time adipose tissues, as well as wildlife reservoirs.

Increased epicardial adipose tissue thickness associated with increased metabolic risk and the presence of heart failure in patients with Chronic Chagas disease

BACKGROUND

It has been described that Trypanosoma cruzi is capable of promoting metabolic disturbances currently considered as cardiovascular risk factors. Moreover, it has been observed that the protozoa can remain in adipose tissue and alter its immune endocrine functions. The aim of this study was to characterize the thickness of epicardial adipose tissue (EAT) in patients with chronic Chagas disease (CCD) concerning their cardiovascular metabolic risk profile compared with those without CCD.

METHODS

A cross-sectional study was performed including T. cruzi seropositive individuals categorized according to a standard CCD classification and a matched seronegative control group. Complete clinical examination, metabolic laboratory tests and transthoracic echocardiography to assess cardiac function and to quantify EAT were performed.

RESULTS

Fifty-five individuals aged 46.7±11.9 y, 34 with CCD and 21 in the control group, were included. The CCD group presented higher EAT thickness in relation to controls (4.54±1.28 vs 3.22±0.99 mm; p=0.001), which was significantly associated with the presence of insulin resistance (OR=3, 95% CI 1.58 to 5.73; p<0.001). This group presented lower levels of plasmatic adiponectin than controls, especially in those patients with EAT ≥4.5 mm (p=0.005) who also presented with heart failure more frequently (p=0.01).

CONCLUSION

In patients with CCD, a higher EAT thickness is observed and is associated with an increased metabolic risk profile indicated mainly by insulin resistance.

Myocardial Involvement in Chagas Disease and Insulin Resistance: A Non-Metabolic Model of Cardiomyopathy

Background:

Heart failure (HF) and type 2 Diabetes Mellitus (T2DM) represent two chronic interrelated conditions accounting for significant morbidity and mortality worldwide. Insulin resistance (IR) has been identified as a risk factor for HF; however, the risk of IR that HF confers has not been well elucidated. The present study aims to analyze the association between myocardial involvement in Chronic Chagas Cardiomyopathy (CCM) and IR, taking advantage of this non-metabolic model of the disease.

Methods:

Cross-sectional study performed during the period 2015–2016. Adults with a serological diagnosis of Chagas disease were included, being divided into two groups: CCM and non-CCM. IR was determined by HOMA-IR index. Bivariate analysis and multivariate logistic regression were performed to determine the association between IR as an outcome and CCM as primary exposure.

Results:

200 patients were included in the study, with a mean age of 54.7 years and a female predominance (53.5%). Seventy-four (37.0%) patients were found to have IR, with a median HOMA-IR index of 3.9 (Q1 = 3.1; Q3 = 5.1). Multiple metabolic variables were significantly associated with IR. In a model analyzing only individuals with an altered HWI, an evident association between CCM and IR was observed (OR 4.08; 95% CI 1.55–10.73, p = 0.004).

Conclusion:

CCM was significantly associated with IR in patients with an altered HWI. The presence of this association in a non-metabolic model of HF (in which the myocardial involvement is expected to be mediated mostly by the parasitic infection) may support the evidence of a direct unidirectional correlation between this last and IR.

The role of fat on cardiomyopathy outcome in mouse models of chronic Trypanosoma cruzi infection

The underlying pathogenic mechanisms of cardiomyopathy in Chagas disease are still unsolved. In order to better clarify the role of fat on the evolution of cardiomyopathy, the present study employed three murine models of chronic Trypanosoma cruzi infection: (1) aP2-RIDα/β transgenic mice (RID mice; an adipose tissue model which express a gain-of-function potent anti-inflammatory activity), (2) allograft inflammatory factor-1 knockout mice (Aif1^-/-), and (3) a Swiss outbred mice. RID mice and non-transgenic mice (wild type, WT) were infected with blood trypomastigotes of Brazil strain. During the acute stage of infection, RID mice had lower parasitemia, lower heart inflammation, and a decrease in the relative distribution of parasite load from cardiac muscle tissue toward epididymal fat. Nevertheless, comparable profiles of myocardial inflammatory infiltrates and relative distribution of parasite load were observed among RID and WT at the chronic stage of infection. Aif1^-/- and Aif1^+/+ mice were infected with bloodstream trypomastigotes of Tulahuen strain and fed with high-fat diet (HFD) or regular diet (RD). Interestingly, Aif1^+/+ HFD infected mice showed the highest mortality. Swiss mice infected with blood trypomastigotes of Berenice-78 strain on a HFD had higher levels of TNFα and more inflammation in their heart tissue than infected mice fed a RD. These various murine models implicate adipocytes in the pathogenesis of chronic Chagas disease and suggest that HFD can lead to a significant increase in the severity of parasite-induced chronic cardiac damage. Furthermore, these data implicate adipocyte TLR4-, TNFα-, and IL-1β-mediated signaling in pro-inflammatory pathways and Aif-1 gene expression in the development of chronic 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.

Immune-neuroendocrine and metabolic disorders in human and experimental T. cruzi infection: New clues for understanding Chagas disease pathology

Studies in mice undergoing acute Trypanosoma cruzi infection and patients with Chagas disease, led to identify several immune-neuroendocrine disturbances and metabolic disorders. Here, we review relevant findings concerning such abnormalities and discuss their possible influence on disease physiopathology.

Metabolic syndrome agravates cardiovascular, oxidative and inflammatory dysfunction during the acute phase of Trypanosoma cruzi infection in mice

We evaluated the influence of metabolic syndrome (MS) on acute Trypanosoma cruzi infection. Obese Swiss mice, 70 days of age, were subjected to intraperitoneal infection with 5 × 102 trypomastigotes of the Y strain. Cardiovascular, oxidative, inflammatory, and metabolic parameters were evaluated in infected and non-infected mice. We observed higher parasitaemia in the infected obese group (IOG) than in the infected control group (ICG) 13 and 15 days post-infection. All IOG animals died by 19 days post-infection (dpi), whereas 87.5% of the ICG survived to 30 days. Increased plasma nitrite levels in adipose tissue and the aorta were observed in the IOG. Higher INF-γ and MCP-1 concentrations and lower IL-10 concentrations were observed in the IOG compared to those in the ICG. Decreased insulin sensitivity was observed in obese animals, which was accentuated after infection. Higher parasitic loads were found in adipose and hepatic tissue, and increases in oxidative stress in cardiac, hepatic, and adipose tissues were characteristics of the IOG group. Thus, MS exacerbates experimental Chagas disease, resulting in greater damage and decreased survival in infected animals, and might be a warning sign that MS can influence other pathologies.

Deficiency of CD73 activity promotes protective cardiac immunity against Trypanosoma cruzi infection but permissive environment in visceral adipose tissue

Damaged cells release the pro-inflammatory signal ATP, which is degraded by the ectonucleotidases CD39 and CD73 to the anti-inflammatory mediator adenosine (ADO). The balance between ATP/ADO is known to determine the outcome of inflammation/infection. However, modulation of the local immune response in different tissues due to changes in the balance of purinergic metabolites has yet to be investigated. Here, we explored the contribution of CD73-derived ADO on the acute immune response against Trypanosoma cruzi parasite, which invades and proliferates within different target tissues. Deficiency of CD73 activity led to an enhanced cardiac microbicidal immune response with an augmented frequency of macrophages with inflammatory phenotype and increased CD8+ T cell effector functions. The increment of local inducible nitric oxide (NO) synthase (iNOS)⁺ macrophages and the consequent rise of myocardial NO production in association with reduced ADO levels induced protection against T. cruzi infection as observed by the diminished cardiac parasite burden compared to their wild-type (WT) counterpart. Unexpectedly, parasitemia was substantially raised in CD73KO mice in comparison with WT mice, suggesting the existence of tissue reservoir/s outside myocardium. Indeed, CD73KO liver and visceral adipose tissue (VAT) showed increased parasite burden associated with a reduced ATP/ADO ratio and the lack of substantial microbicidal immune response. These data reveal that the purinergic system has a tissue-dependent impact on the host immune response against T. cruzi infection.

Advances in understanding the role of adipose tissue and mitochondrial oxidative stress in Trypanosoma cruzi infection

Trypanosoma cruzi, the etiologic agent of Chagas disease, causes a latent infection that results in cardiomyopathy. Infection with this pathogen is a major socio-economic burden in areas of endemic infection throughout Latin America. The development of chagasic cardiomyopathy is dependent on the persistence of this parasite in host tissues. Pathogenesis of this cardiomyopathy is multifactorial and research indicates that it includes microvascular dysfunction, immune responses to host and parasite antigens, and various vasoactive and lipid mediators produced by both the host and parasite. It has been demonstrated that T. cruzi persists in adipose tissue and uses fat as a nutritional niche in infected hosts. This chronic infection of adipose tissue plays an important role in the pathogenesis and persistence of this infection and involves mitochondrial stress responses as well as the production of various anti-inflammatory adipokines and pro-inflammatory cytokines by both white and brown adipose tissue. The changes in diet in endemic regions of infection have resulted in an epidemic of obesity that has significant implications for the pathogenesis of T. cruzi infection and the development of chagasic cardiomyopathy in infected humans.

Isolation and Phenotypic Characterization of Inflammatory Cells from Clinical Samples: Purification of Macrophages from Trypanosoma cruzi-Infected Hearts

Trypanosoma cruzi, the causal agent of chronic Chagas cardiomyopathy, exhibits an important tropism for cardiac tissue. In consequence, T. cruzi experimental infection represents a unique model to study cardiac macrophage behavior and effector functions during either acute or chronic immune response. In this chapter we describe a protocol to isolate immune cells from T. cruzi-infected murine cardiac tissue and to determine the percentage, absolute number, phenotype, and functionality of monocytes and macrophages by using flow cytometry. Moreover, we describe the parameters to discriminate between resident and infiltrating mononuclear phagocytic cells within infected hearts. The investigations in this field will provide mechanistic insights about the roles of these innate immune cells in the context of a clinically relevant target tissue.

Hemozoin-induced activation of human monocytes toward M2-like phenotype is partially reversed by antimalarial drugs-chloroquine and artemisinin

Plasmodium falciparum malaria is the most severe form of malaria with several complications. The malaria pigment‐hemozoin (Hz) is associated with severe anemia, cytokine dysfunction, and immunosuppression, thus making it an interesting target for developing new strategies for antimalarial therapy. Monocytes (MO) in circulation actively ingest Hz released by Plasmodium parasites and secrete pro‐ and anti‐inflammatory cytokines. M1 and M2 types represent the two major forms of MO/macrophages (MQ) with distinct phenotypes and opposing functions. Imbalance in the polarization of these types is reported in many infectious diseases. Though the association of Hz with immunosuppression is well documented, its role in activation of MO in context of M1/M2 phenotypes remains to be addressed. We report here that natural Hz drives human MO toward M2‐like phenotype as evidenced by the expression of M2 signature markers. Hz‐fed MO showed elevated transcript and secreted level of IL‐10, CCL17, CCL1, expression of mannose‐binding lectin receptor (CD206), and arginase activity. Hz attenuated HLA‐DR expression, nitric oxide, and reactive oxygen species production, which are the features of M1 phenotype. Our data also implicate the involvement of p38 MAPK, PI3K/AKT, and NF‐κB signaling pathways in skewing of Hz‐fed MO toward M2‐like type and suppression of mitogen‐stimulated lymphocyte proliferation. Importantly, antimalarial drugs—chloroquine and artemisinin—partially reversed activation of Hz‐induced MO toward M2‐like phenotype. Considering the limitations in the current therapeutic options for malaria, we propose that these drugs may be re‐examined for their potential as immunomodulators and candidates for adjunctive treatment in malaria.

Chlamydia pneumoniae Infection Exacerbates Atherosclerosis in ApoB100only/LDLR-/- Mouse Strain

Aims

Hyperlipidaemia model animals have been used to elucidate the role of Chlamydia pneumoniae (Cpn) infection in atherosclerosis. The aims of this study were to investigate the proatherogenic effect of multiple Cpn infections in ApoB100only/LDLR^−/− mice which based on lipid profile can be regarded as the most suitable mouse model of human hypercholesterolemia and to compare the lesion development to that in a major atherosclerosis model ApoE^−/− mice.

Methods and Results

Aorta samples of ApoB100only/LDLR^−/− mice infected three times with Cpn were subjected to morphometric analyses. Morphometric evaluation disclosed that Cpn infections exacerbated atherosclerosis development in the aortic root and descending aorta of the mice fed with normal diet. Viable Cpn was detected in the ascending aorta by RT-PCR. Chlamydial 16SrRNA expression showed the presence of viable Cpn in the aorta of infected animals. A similar rate of acceleration of atherosclerosis was observed when the infection protocol was applied in ApoB100only/LDLR^−/− and in ApoE^−/− mice.

Conclusion

Similar to ApoE^−/− mice, ApoB100only/LDLR^−/− mice with more human-relevant serum lipoprotein composition develop increased atherosclerosis after Cpn infections; thus this mouse strain can be used as a model of infection-related atherosclerosis enhancement and can provide further evidence for the proatherogenic influence of Cpn in mice.

Regulatory Lymphoid and Myeloid Cells Determine the Cardiac Immunopathogenesis of Trypanosoma cruzi Infection

Chagas disease is a multisystemic disorder caused by the protozoan parasite Trypanosoma cruzi, which affects ~8 million people in Latin America, killing 7,000 people annually. Chagas disease is one of the main causes of death in the endemic area and the leading cause of infectious myocarditis in the world. T. cruzi infection induces two phases, acute and chronic, where the infection is initially asymptomatic and the majority of patients will remain clinically indeterminate for life. However, over a period of 10–30 years, ~30% of infected individuals will develop irreversible, potentially fatal cardiac syndromes (chronic chagasic cardiomyopathy [CCC]), and/or dilatation of the gastro-intestinal tract (megacolon or megaesophagus). Myocarditis is the most serious and frequent manifestation of chronic Chagas heart disease and appears in about 30% of infected individuals several years after infection occurs. Myocarditis is characterized by a mononuclear cell infiltrate that includes different types of myeloid and lymphoid cells and it can occur also in the acute phase. T. cruzi infects and replicates in macrophages and cardiomyocytes as well as in other nucleated cells. The pathogenesis of the chronic phase is thought to be dependent on an immune-inflammatory reaction to a low-grade replicative infection. It is known that cytokines produced by type 1 helper CD4+ T cells are able to control infection. However, the role that infiltrating lymphoid and myeloid cells may play in experimental and natural Chagas disease pathogenesis has not been completely elucidated, and several reports indicate that it depends on the mouse genetic background and parasite strain and/or inoculum. Here, we review the role that T cell CD4+ subsets, myeloid subclasses including myeloid-derived suppressor cells may play in the immunopathogenesis of Chagas disease with special focus on myocarditis, by comparing results obtained with different experimental animal models.

Role of Hormonal Circuitry Upon T Cell Development in Chagas Disease: Possible Implications on T Cell Dysfunctions

T cell response plays an essential role in the host resistance to infection by the protozoan parasite Trypanosoma cruzi, the causative agent of Chagas disease. This infection is often associated with multiple manifestations of T cell dysfunction, both during the acute and the chronic phases of disease. Additionally, the normal development of T cells is affected. As seen in animal models of Chagas disease, there is a strong thymic atrophy due to massive death of CD4⁺CD8⁺ double-positive cells by apoptosis and an abnormal escape of immature and potentially autoreactive thymocytes from the organ. Furthermore, an increase in the release of corticosterone triggered by T. cruzi-driven systemic inflammation is strongly associated with the alterations seen in the thymus of infected animals. Moreover, changes in the levels of other hormones, including growth hormone, prolactin, and testosterone are also able to contribute to the disruption of thymic homeostasis secondary to T. cruzi infection. In this review, we discuss the role of hormonal circuits involved in the normal T cell development and trafficking, as well as their role on the thymic alterations likely related to the peripheral T cell disturbances largely reported in both chagasic patients and animal models of Chagas disease.

Metabolic Crosstalk Between Host and Parasitic Pathogens

A complex network that embraces parasite-host intrinsic factors and the microenvironment regulated the interaction between a parasite and its host. Nutritional pressures exerted by both elements of this duet thus dictate this host-parasite niche. To survive and proliferate inside a host and a harsh nutritional environment, the parasites modulate different nutrient sensing pathways to subvert host metabolic pathways. Such mechanism is able to change the flux of distinct nutrients/metabolites diverting them to be used by the parasites. Apart from this nutritional strategy, the scavenging of nutrients, particularly host fatty acids, constitutes a critical mechanism to fulfil parasite nutritional requirements, ultimately defining the host metabolic landscape. The host metabolic alterations that result from host-parasite metabolic coupling can certainly be considered important targets to improve diagnosis and also for the development of future therapies. Metabolism is in fact considered a key element within this complex interaction, its modulation being crucial to dictate the final infection outcome.

Augmentation of hypoxia-inducible factor-1-alpha in reinfused blood cells enhances diabetic ischemic wound closure in mice

Diabetes-associated dysfunction in angiogenesis predominantly contributes to impairment of wound closure, but a role of hypoxia-inducible factor 1 alpha (HIF-1a) in the process remain poorly understood. Here, we examined whether expression of HIF-1a in re-infused blood cells may improve the diabetic wound closure in mice. We found that that expression of HIF-1a in re-infused isogeneic blood cells significantly improved diabetic wound healing in mice, seemingly through augmentation of wound-associated angiogenesis. Mechanistically, expression of HIF-1a in re-infused blood cells significantly increased macrophage infiltration at the wound site, and macrophages produced vascular endothelial growth factor A (VEGF-A) to promote wound-associated angiogenesis. Together, our data suggest that augmentation of HIF-1a in reinfused blood cells may enhance diabetic ischemic wound closure.

Adipose Tissue-Specialized Immunologic Features Might Be the Potential Therapeutic Target of Prospective Medicines for Obesity

Excessive lipid accumulation in adipose tissue is either the source of obesity or the cause and result of chronic local inflammation, and recent studies indicate that the accumulation may induce many other specialized immunologic features with macrophages and epidemic diseases. We analyze the effective stages of immune cells in adipose tissue, including macrophage recruitment, macrophage polarization, and macrophage-like phenotype preadipocyte possession to find optimal sites as drug targets. Subsequently, some main signaling pathways are summarized in this review, including the AMP-activated protein kinase (AMPK) pathway, the JNK signaling pathway, and a novel one, the Notch signaling pathway. We illustrate all these points in order to determine the general pathogenesis of chronic low-grade local inflammation in adipose tissue and the related signaling pathways. In addition, signal-associated prospective compounds, such as berberine, are summarized and discussed with potential targets in pathogenesis. This might provide some possible thoughts and novel therapies for studying chronic inflammatory diseases, such as insulin resistance and type 2 diabetes mellitus.

Alterations in pancreatic β cell function and Trypanosoma cruzi infection: evidence from human and animal studies

The parasite Trypanosoma cruzi causes a persistent infection, Chagas disease, affecting millions of persons in endemic areas of Latin America. As a result of immigration, this disease has now been diagnosed in non-endemic areas worldwide. Although, the heart and gastrointestinal tract are the most studied, the insulin-secreting β cell of the endocrine pancreas is also a target of infection. In this review, we summarize available clinical and laboratory evidence to determine whether T. cruzi-infection-mediated changes of β cell function is likely to contribute to the development of hyperglycemia and diabetes. Our literature survey indicates that T. cruzi infection of humans and of experimental animals relates to altered secretory behavior of β cells. The mechanistic basis of these observations appears to be a change in stimulus-secretion pathway function rather than the loss of insulin-producing β cells. Whether this attenuated insulin release ultimately contributes to the pathogenesis of diabetes in human Chagas disease, however, remains to be determined. Since the etiologies of diabetes are multifactorial including genetic and lifestyle factors, the use of cell- and animal-based investigations, allowing direct manipulation of these factors, are important tools in testing if reduced insulin secretion has a causal influence on diabetes in the setting of Chagas disease. Long-term clinical investigations will be required to investigate this link in humans.

Adipose Tissue: A Safe Haven for Parasites?

Adipose tissue (AT) is no longer regarded as an inert lipid storage, but as an important central regulator in energy homeostasis and immunity. Three parasite species are uniquely associated with AT during part of their life cycle: Trypanosoma cruzi, the causative agent of Chagas disease; Trypanosoma brucei, the causative agent of African sleeping sickness; and Plasmodium spp., the causative agents of malaria. In AT, T. cruzi resides inside adipocytes, T. brucei is found in the interstitial spaces between adipocytes, while Plasmodium spp. infect red blood cells, which may adhere to the blood vessels supplying AT. Here, we discuss how each parasite species adapts to this tissue environment and what the implications are for pathogenesis, clinical manifestations, and therapy.

Hyperglycemia induces mixed M1/M2 cytokine profile in primary human monocyte-derived macrophages

Hyperglycaemia is a key factor in diabetic pathology. Macrophages are essential regulators of inflammation which can be classified into two major vectors of polarisation: classically activated macrophages (M1) and alternatively activated macrophages (M2). Both types of macrophages play a role in diabetes, where M1 and M2-produced cytokines can have detrimental effects in development of diabetes-associated inflammation and diabetic vascular complications. However, the effect of hyperglycaemia on differentiation and programming of primary human macrophages was not systematically studied. We established a unique model to assess the influence of hyperglycaemia on M1 and M2 differentiation based on primary human monocyte-derived macrophages. The effects of hyperglycaemia on the gene expression and secretion of prototype M1 cytokines TNF-alpha and IL-1beta, and prototype M2 cytokines IL-1Ra and CCL18 were quantified by RT-PCR and ELISA. Hyperglycaemia stimulated production of TNF-alpha, IL-1beta and IL-1Ra during macrophage differentiation. The effect of hyperglycaemia on TNF-alpha was acute, while the stimulating effect on IL-1beta and IL-1Ra was constitutive. Expression of CCL18 was supressed in M2 macrophages by hyperglycaemia. However the secreted levels remained to be biologically significant. Our data indicate that hyperglycaemia itself, without additional metabolic factors induces mixed M1/M2 cytokine profile that can support of diabetes-associated inflammation and development of vascular complications.