Trypanosoma cruzi infection of cultured adipocytes results in an inflammatory phenotype

Infection with Trypanosoma cruzi, the etiologic agent of Chagas disease is accompanied by an intense inflammatory reaction. Our laboratory group has identified adipose tissue as one of the major sites of inflammation during disease progression. Because adipose tissue is composed of many cell types, we were interested in investigating whether the adipocyte per se was a source of inflammatory mediators in this infection. Cultured adipocytes were infected with the Tulahuen strain of T. cruzi for 48-96 h. Immunoblot and quantitative PCR (qPCR) analyses demonstrated an increase in the expression of proinflammatory cytokines and chemokines, including interleukin (IL)-1 beta, interferon-gamma, tumor necrosis factor-alpha, CCL2, CCL5, and CXCL10 as well as an increase in the expression of Toll-like receptors-2 and 9 and activation of the notch pathway. Interestingly, caveolin-1 expression was reduced while cyclin D1 and extracellular signal-regulated kinase (ERK) expression was increased. The expression of PI3kinase and the activation of AKT (phosphorylated AKT) were increased suggesting that infection may induce components of the insulin/IGF-1 receptor cascade. There was an infection-associated decrease in adiponectin and peroxisome proliferator-activated receptor-gamma (PPAR-gamma). These data provide a mechanism for the increase in the inflammatory phenotype that occurs in T. cruzi-infected adipocytes. Overall, these data implicate the adipocyte as an important target of T. cruzi, and one which contributes significantly to the inflammatory response observed in Chagas disease.

Regulation of host cell cyclin D1 by Trypanosoma cruzi in myoblasts

Infection with the parasite Trypanosoma cruzi causes Chagas disease. In this study we demonstrated that there was an increase in cyclin D1 expression in T. cruzi (Tulahuen strain)-infected myoblasts. To examine a possible mechanism for the increased cyclin D1 expression we transfected L(6)E(9) myoblasts with cyclin D1 luciferase reporter constructs and infected with T. cruzi. There was no evidence of an increase in promoter activity. Additionally, quantitative PCR did not demonstrate any change in cyclin D1 message during infection. Moreover, we demonstrated that the cyclin D1 protein was significantly stabilized after infection. Collectively, these data indicate that infection with T. cruzi increases cyclin D1 protein abundance post-translationally.

Thromboxane A2 is a key regulator of pathogenesis during Trypanosoma cruzi infection

Chagas' disease is caused by infection with the parasite Trypanosoma cruzi. We report that infected, but not uninfected, human endothelial cells (ECs) released thromboxane A(2) (TXA(2)). Physical chromatography and liquid chromatography-tandem mass spectrometry revealed that TXA(2) is the predominant eicosanoid present in all life stages of T. cruzi. Parasite-derived TXA(2) accounts for up to 90% of the circulating levels of TXA(2) in infected wild-type mice, and perturbs host physiology. Mice in which the gene for the TXA(2) receptor (TP) has been deleted, exhibited higher mortality and more severe cardiac pathology and parasitism (fourfold) than WT mice after infection. Conversely, deletion of the TXA(2) synthase gene had no effect on survival or disease severity. TP expression on somatic cells, but not cells involved in either acquired or innate immunity, was the primary determinant of disease progression. The higher intracellular parasitism observed in TP-null ECs was ablated upon restoration of TP expression. We conclude that the host response to parasite-derived TXA(2) in T. cruzi infection is possibly an important determinant of mortality and parasitism. A deeper understanding of the role of TXA(2) may result in novel therapeutic targets for a disease with limited treatment options.

Immune dysfunction in caveolin-1 null mice following infection with Trypanosoma cruzi (Tulahuen strain)

In recent years, host cell caveolae/caveolins have emerged as potentially important targets for pathogenic microorganisms; therefore, we investigated the role of caveolin-1 (Cav-1) in T. cruzi infection using Cav-1 null mice. Cav-1 null and wild type mice were infected with the virulent Tulahuen strain. The mortality was 100% in both groups, but death was slightly delayed in wild type mice. The parasitemia in the Cav-1 null mice was significantly reduced compared with wild type littermates. Histopathologic examination of the heart revealed numerous pseudocysts, myonecrosis, and marked inflammation, which was similar in both mouse groups. Real-time PCR confirmed these observations. Infection of cultured cardiac fibroblasts obtained from Cav-1 null and wild type mice revealed no differences in infectivity. Determination of serum levels of several inflammatory mediators revealed a striking reduction in IFN-gamma, TNF-alpha and components of the nitric oxide pathway in infected Cav-1 null mice. Infection of wild type mice resulted in the expected enhancement of inflammatory mediators. The defective production of chemokines and cytokines observed in vivo is in part attributed to Cav-1 null macrophages. Despite these marked differences in the response to infection by inflammatory mediators between the two mouse strains, the final outcome was similar. These results suggest that Cav-1 may play an important role in the normal development of immune responses.

The adipocyte as an important target cell for Trypanosoma cruzi infection

Adipose tissue plays an active role in normal metabolic homeostasis as well as in the development of human disease. Beyond its obvious role as a depot for triglycerides, adipose tissue controls energy expenditure through secretion of several factors. Little attention has been given to the role of adipocytes in the pathogenesis of Chagas disease and the associated metabolic alterations. Our previous studies have indicated that hyperglycemia significantly increases parasitemia and mortality in mice infected with Trypanosoma cruzi. We determined the consequences of adipocyte infection in vitro and in vivo. Cultured 3T3-L1 adipocytes can be infected with high efficiency. Electron micrographs of infected cells revealed a large number of intracellular parasites that cluster around lipid droplets. Furthermore, infected adipocytes exhibited changes in expression levels of a number of different adipocyte-specific or adipocyte-enriched proteins. The adipocyte is therefore an important target cell during acute Chagas disease. Infection of adipocytes by T. cruzi profoundly influences the pattern of adipokines. During chronic infection, adipocytes may represent an important long-term reservoir for parasites from which relapse of infection can occur. We have demonstrated that acute infection has a unique metabolic profile with a high degree of local inflammation in adipose tissue, hypoadiponectinemia, hypoglycemia, and hypoinsulinemia but with relatively normal glucose disposal during an oral glucose tolerance test.

Trypanosoma cruzi infection activates extracellular signal-regulated kinase in cultured endothelial and smooth muscle cells

Trypanosoma cruzi infection causes cardiomyopathy and vasculopathy. We examined the consequence of this infection for the mitogen-activated protein kinase (MAPK) pathways, which regulate cell proliferation in cultured human umbilical vein endothelial and vascular smooth muscle cells. Infection of these cells resulted in activation of extracellular signal-regulated kinases 1and 2 (ERK1/2) but not c-Jun N-terminal kinase or p38 MAPK. Treatment of these cells with the MAPK kinase inhibitor PD98059 prior to infection blocked the increase in phosphorylated ERK1/2 seen with infection. Heat-killed parasites did not activate ERK1/2, indicating that activation of ERK1/2 was dependent on infection of these cells by live parasites. Furthermore, transfection with dominant-negative Raf(301) or Ras(N17) constructs reduced the infection-associated levels of phospho-ERK1/2, indicating that the activation of ERK1/2 involved the Ras-Raf-ERK pathway. Infection also resulted in an increase in activator protein 1 (AP-1) activity, which was inhibited by transfection with a dominant-negative Raf(301) construct. T. cruzi-infected endothelial cells secreted endothelin-1 and interleukin-1beta, which activated ERK1/2 and induced cyclin D1 expression in uninfected smooth muscle cells. These data suggest a possible molecular paradigm for the pathogenesis of the vasculopathy and the cardiovascular remodeling associated with T. cruzi infection.

Infection of endothelial cells with Trypanosoma cruzi activates NF-kappaB and induces vascular adhesion molecule expression

Transcriptional activation of vascular adhesion molecule expression, a major component of an inflammatory response, is regulated, in part, by the nuclear factor-kappaB/Rel (NF-kappaB) family of transcription factors. We therefore determined whether Trypanosoma cruzi infection of endothelial cells resulted in the activation of NF-kappaB and the induction or increased expression of adhesion molecules. Human umbilical vein endothelial cells (HUVEC) were infected with trypomastigotes of the Tulahuen strain of T. cruzi. Electrophoretic mobility shift assays with an NF-kappaB-specific oligonucleotide and nuclear extracts from T. cruzi-infected HUVEC (6 to 48 h postinfection) detected two major shifted complexes. Pretreatment with 50x cold NF-kappaB consensus sequence abolished both gel-shifted complexes while excess SP-1 consensus sequence had no effect. These data indicate that nuclear extracts from T. cruzi-infected HUVEC specifically bound to the NF-kappaB consensus DNA sequence. Supershift analysis revealed that the gel-shifted complexes were comprised of p65 (RelA) and p50 (NF-kappaB1). Northern blot analyses demonstrated both the induction of vascular cell adhesion molecule 1 and E-selectin and the upregulation of intercellular adhesion molecule 1 mRNA in HUVEC infected with T. cruzi. Immunocytochemical staining confirmed adhesion molecule expression in response to T. cruzi infection. These findings are consistent with the hypothesis that the activation of the NF-kappaB pathway in endothelial cells associated with T. cruzi infection may be an important factor in the inflammatory response and subsequent vascular injury and endothelial dysfunction that lead to chronic cardiomyopathy.

Application of cardiac gated magnetic resonance imaging in murine Chagas' disease

To evaluate the role of gated cardiac magnetic imaging resonance (MRI) in Chagas' disease, we infected mice with Trypanosoma cruzi (Brazil strain). Two models were chosen for study, the CD1 and the inducible nitric oxide synthase knockout (NOS2-/-) mice. Infection of CD1 mice was associated with a significant increase in the right ventricular inner diameter (RVID) that was reversed in some mice by verapamil. Expression of cardiac NOS2 has been associated with myocardial dysfunction. Therefore, we evaluated chagasic cardiomyopathy in NOS2-/- and syngeneic wild type (WT) mice. Infected WT mice exhibited an increase in RVID in the acute phase (< 60 days postinfection) that was more marked during chronic infection (>100 days postinfection). Chronically infected NOS2-/- mice had an increase in RVID. The RVID in infected WT mice was greater than in NOS2-/- mice. These data demonstrate that MRI is a useful tool in the serial evaluation of the heart in murine Chagas' disease. In addition, it supports the notion that the NOS2-/-/NO pathway may contribute to the pathogenesis of murine chagasic cardiomyopathy.

The putative mechanistic basis for the modulatory role of endothelin-1 in the altered vascular tone induced by Trypanosoma cruzi

Chagas' disease, caused by Trypanosoma cruzi, is an important cause of heart disease in Latin America. T. cruzi-induced microvascular compromise, in turn, is thought to play a major role in chagasic heart disease. Previous in vitro studies have implicated endothelin-1 (ET-1) as a potentially important vasomodulator present in increased levels in the supernatant of T. cruzi infected cultured human umbilical vein endothelial cells (HUVEC). Thus, the goal of the present investigation was to further evaluate the potentially important contribution of ET-1 to T. cruzi-induced alterations in vascular tone in vitro. Bioassay studies once again documented that exposure of isolated rat aortic rings to infected HUVEC supernatants elicited contractile responses whose steady-state magnitude was significantly greater than contractile responses elicited by exposure of aortic rings to uninfected HUVEC supernatants. Furthermore, the increased aortic contractility was significantly attenuated by the presence of the ET(A) subtype selective antagonists BMS-182,874 or BQ-123. Additionally, incubation of HUVEC with either verapamil or phosphoramidon prior to infection was also associated with reduced aortic contractility, upon exposure to the supernatant. Phosphoramidon, but not verapamil, produced a significant decrease in the measured ET-1 levels in the HUVEC supernatant. Consistent with the bioassay results, preincubation of Fura-2-loaded cultured rat aortic vascular smooth muscle cells with verapamil resulted in a near complete ablation of ET-1-induced transmembrane Ca2+ flux. Taken together, these data are consistent with the hypothesis that ET-1-induced vasoconstriction may play an important modulatory role in the vascular compromise characteristic of T. cruzi infection.

Expression of cardiac cytokines and inducible form of nitric oxide synthase (NOS2) in Trypanosoma cruzi-infected mice

Expression of Cardiac Cytokines and Inducible Form of Nitric Oxide Synthase (NOS2) in Trypanosoma cruzi-infected Mice. Journal of Molecular and Cellular Cardiology (1999) 31, 75-88. Both cardiac cytokine and inducible nitric oxide synthase (NOS2) expression have been implicated in the cardiac dysfunction associated with myocarditis and cardiomyopathy. Chagas' disease, caused by Trypanosoma cruzi, is an important cause of cardiomyopathy. We examined the effect of T. cruzi (Brazil strain) infection with or without verapamil treatment on the expression of cytokines and NOS2 in the heart. Messenger RNA for NOS2, IL-1beta, and TNF-alpha was induced in the myocardium of infected mice, and Western blot analysis as well as immunohistochemistry demonstrated a significant increase in NOS2 protein. Verapamil treatment reduced the expression of cardiac NOS2 protein and the mRNAs for NOS2, TNF-alpha, and IL-1beta. Infection-associated increases in cardiac L-citrulline were also reduced by verapamil treatment. Verapamil-treated infected mice that survived for 80 days exhibited less inflammation and fibrosis compared to untreated mice. Gated MRI and echocardiography revealed an increased right ventricular inner diameter (RVID) in untreated but not in verapamil-treated infected CD1 mice. This suggests that the infection-associated expression of cytokines and NOS2 in the heart correlate with the severity of myocarditis and the effect of verapamil. The RVID was significantly increased in infected wild-type (WT) compared to infected syngeneic NOS2 knockout (NOS2-/-) mice. Fractional shortening was decreased and myocardial L-citrulline was increased in infected WT mice. These data suggest that NO generated from cardiac NOS2 may participate in the pathogenesis of murine chagasic heart disease.