Trypanosoma cruzi infection affects actin mRNA regulation in heart muscle cells

Trypanosoma cruzi down-regulates mechanosensitive proteins in cardiomyocytes

BACKGROUND

Cardiac physiology depends on coupling and electrical and mechanical coordination through the intercalated disc. Focal adhesions offer mechanical support and signal transduction events during heart contraction-relaxation processes. Talin links integrins to the actin cytoskeleton and serves as a scaffold for the recruitment of other proteins, such as paxillin in focal adhesion formation and regulation. Chagasic cardiomyopathy is caused by infection by Trypanosoma cruzi and is a debilitating condition comprising extensive fibrosis, inflammation, cardiac hypertrophy and electrical alterations that culminate in heart failure.

OBJECTIVES

Since mechanotransduction coordinates heart function, we evaluated the underlying mechanism implicated in the mechanical changes, focusing especially in mechanosensitive proteins and related signalling pathways during infection of cardiac cells by T. cruzi.

METHODS

We investigated the effect of T. cruzi infection on the expression and distribution of talin/paxillin and associated proteins in mouse cardiomyocytes in vitro by western blotting, immunofluorescence and quantitative real-time polymerase chain reaction (qRT-PCR).

FINDINGS

Talin and paxillin spatial distribution in T. cruzi-infected cardiomyocytes in vitro were altered associated with a downregulation of these proteins and mRNAs levels at 72 h post-infection (hpi). Additionally, we observed an increase in the activation of the focal adhesion kinase (FAK) concomitant with increase in β-1-integrin at 24 hpi. Finally, we detected a decrease in the activation of FAK at 72 hpi in T. cruzi-infected cultures.

MAIN CONCLUSION

The results suggest that these changes may contribute to the mechanotransduction disturbance evidenced in chagasic cardiomyopathy.

Trypanosoma cruzi activates mouse cardiac fibroblasts in vitro leading to fibroblast-myofibroblast transition and increase in expression of extracellular matrix proteins

Background

Cardiac fibrosis is a consequence of chronic chagasic cardiomyopathy (CCC). In other cardiovascular diseases, the protagonist role of fibroblasts in cardiac fibrosis is well established. However, the role of cardiac fibroblasts (CFs) in fibrosis during the CCC is not clear. Here, our aim was to investigate the effect of Trypanosoma cruzi, the etiological agent of Chagas disease on CFs activation.

Methods

Cardiac fibroblasts were purified from primary cultures of mouse embryo cardiac cells. After two passages, cells were infected with T. cruzi (Y strain) and analyzed at different times for determination of infectivity, activation and production of extracellular matrix components (fibronectin, laminin and collagen IV) by immunofluorescence and western blot.

Results

At second passage, cultures were enriched in CFs (95% of fibroblasts and 5% of cardiomyocytes), as revealed by presence of alpha-smooth muscle actin (α-SMA) and discoidin domain receptor 2 (DDR2) and absence of sarcomeric tropomyosin (ST) protein expression. Trypanosoma cruzi infection induced fibroblast-myofibroblast transition, with increased expression of α-SMA after 6 and 24 h post-infection (hpi). Fibronectin was increased at 6, 24 and 48 hpi, laminin was increased at 6 and 24 hpi and collagen IV was increased at 6 hpi.

Conclusions

Our results showed that T. cruzi activates CFs, inducing activation and exacerbates ECM production. Furthermore, our data raise the possibility of the involvement of CFs in heart fibrosis during Chagas disease.

Current understanding of the Trypanosoma cruzi-cardiomyocyte interaction

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

Disarray of sarcomeric alpha-actinin in cardiomyocytes infected by Trypanosoma cruzi

Infection with Trypanosoma cruzi causes acute myocarditis and chronic cardiomyopathy. Remarkable changes have been demonstrated in the structure and physiology of cardiomyocytes during infection by this parasite that may contribute to the cardiac dysfunction observed in Chagas' disease. We have investigated the expression of alpha-actinin, an actin-binding protein that plays a key role in the formation and maintenance of Z-lines, during the T. cruzi-cardiomyocyte interaction in vitro. Immunolocalization of alpha-actinin in control cardiomyocytes demonstrated a typical periodicity in the Z line of cardiac myofibrils, as well as its distribution at focal adhesion sites and along the cell-cell junctions. No significant changes were observed in the localization of alpha-actinin after 24 h of infection. In contrast, depletion of sarcomeric distribution of alpha-actinin occurred after 72 h in T. cruzi-infected cardiomyocytes, while no change occurred at focal adhesion contacts. Biochemical assays demonstrated a reduction of 46% and 32% in the expression of alpha-actinin after 24 h and 72 h of infection, respectively. Intracellular parasites were also stained with an anti-alpha-actinin antibody that recognized a protein of 78 kDa by Western blot. Taken together, our data demonstrate a degeneration of the myofibrils in cardiomyocytes induced by T. cruzi infection, rather than a disassembly of the I bands within sarcomeres.

Trypanosoma cruzi disrupts myofibrillar organization and intracellular calcium levels in mouse neonatal cardiomyocytes

Immunofluorescence studies of normal and Trypanosoma cruzi-infected primary cultures of heart muscle cells were performed to gather information about the arrangement of myofibrillar components during the intracellular life cycle of this parasite. By using a panel of monoclonal antibodies against various myofibrillar proteins, a progressive disruption and loss of contractile proteins (such myosin and actin) of the host cell was detected during infection. The host cell formed a loose network of myofibrillar proteins around the parasites. Breakdown of the myofibrils occurred in regions where the parasites were present, and heavily infected cells showed myofibrillar proteins at their periphery. In parallel, we investigated the effect of T. cruzi infection on intracellular calcium levels by using a Ca2+ fluorescent indicator (confocal microscopy). Infected cardiomyocytes displayed a marked impairment in contractility, and calcium influxes became irregular and less intense when compared with those of non-infected cells. Our results demonstrate that T. cruzi infection dramatically affects calcium fluxes and causes myofibrillar breakdown disturbing cardiomyocyte contractility.

Trypanosoma cruzi infection disrupts vinculin costameres in cardiomyocytes

Chagas' disease cardiomyopathy is an important manifestation of Trypanosoma cruzi infection, leading to cardiac dysfunction and serious arrhythmias. We have here investigated by indirect immunofluorescence assay the distribution of vinculin, a focal adhesion protein with a major role in the transmission of contraction force, during the T. cruzi-cardiomyocyte infection in vitro and in vivo. No change in vinculin distribution was observed after 24 h of infection, where control and T. cruzi-infected cardiomyocytes displayed vinculin localized at costameres and intercalated discs. On the other hand, a clear disruption of vinculin costameric distribution was noted after 72 h of infection. A significant reduction in the levels of vinculin expression was observed at all times of infection. In murine experimental Chagas' disease, alteration in the vinculin distribution was also detected in the infected myocardium, with no costameric staining in infected myocytes and irregular alignment of intercalated discs in cardiac fibers. These data suggest that the disruption of costameric vinculin distribution and the enlargement of interstitial space due to inflammatory infiltration may contribute to the reduction of transmission of cardiac contraction force, leading to alterations in the heart function in Chagas' disease.

Endocytic pathway in mouse cardiac cells

Primary cultures of heart muscle cells provide powerful tools for cardiac cell biological research that permits both physiological and biochemical approaches. In the present study we analyzed the endocytosis of cardiac cells and presented morphological characterization of the endocytic machinery using markers, which enabled us to follow the fluid-phase, receptor-mediated endocytosis and the internalization of large particles. Our results demonstrated the route of the internalized cargo to early endosomes followed or not by its discharge in the late compartments. We also confirmed the ability of cardiac muscle cells to ingest large particles such as the mannosylated ligand zymosan A, and even internalize whole eukaryotic cells such as the protozoan parasite Trypanosoma cruzi. Since endocytosis is involved in many important cellular functions, the present work contributes to the knowledge of possible additional roles played by cardiac muscle cells besides their well known ability to act as physically energetic cells in the body, constantly contracting without tiring.

Trypanosoma cruzi: acute infection affects expression of alpha-2-macroglobulin and A2MR/LRP receptor differently in C3H and C57BL/6 mice

Although a complete cellular and humoral immune response is elicited in Chagas' disease, recent data suggest that other natural elements of innate immunity may also contribute to the initial host primary defense. alpha-Macroglobulins are a family of plasma proteinase inhibitors that are acute-phase reactants in Trypanosoma cruzi-infected mice and humans. Mice contain a tetrameric alpha-2-macroglobulin (MAM) and a monomeric murinoglobulin (MUG). Heterogeneity in their reactions was observed in murine T. cruzi-infected plasma A2M levels despite an overall increase. In addition, up-regulation of the A2M receptor (A2MR/LRP) was observed in peritoneal macrophages during T. cruzi infection. Here, we show that during T. cruzi infection (Y strain), the MAM and MUG hepatic mRNA levels and the corresponding plasma protein levels were up-regulated in C3H and C57BL/6 (B6) mice, but with different kinetics. On the contrary, A2MR/LRP mRNA levels increased in acutely infected C3H mice, but decreased in B6 mice, in both liver and heart. Immunocytochemistry of infected B6 heart cryosections confirmed a less intense endothelium labeling by the fluoresceinated ligand for A2MR/LRP. On the other hand, infected B6 spleen cells displayed higher F-A2M-FITC binding and MAC1 expression, confirming higher A2MR/LRP expression in macrophages. In uninfected mice, as well as after T. cruzi infection, higher A2M plasma levels were measured in C3H mice than in B6 mice. The lower tissue T. cruzi parasitism found in C3H-infected mice could reflect an inhibitory effect of A2M on parasite invasion. Our present data further contribute to clarifying aspects of the role of A2MR/LRP in a model of acute Chagas' disease in different mouse strains.