Trypanosoma cruzi infection induces microfilament depletion in human placenta syncytiotrophoblast

Modeling the Ruminant Placenta-Pathogen Interactions in Apicomplexan Parasites: Current and Future Perspectives

Neospora caninum and Toxoplasma gondii are one of the main concerns of the livestock sector as they cause important economic losses in ruminants due to the reproductive failure. It is well-known that the interaction of these parasites with the placenta determines the course of infection, leading to fetal death or parasite transmission to the offspring. However, to advance the development of effective vaccines and treatments, there are still important gaps on knowledge on the placental host-parasite interactions that need to be addressed. Ruminant animal models are still an indispensable tool for providing a global view of the pathogenesis, lesions, and immune responses, but their utilization embraces important economic and ethics restrictions. Alternative in vitro systems based on caruncular and trophoblast cells, the key cellular components of placentomes, have emerged in the last years, but their use can only offer a partial view of the processes triggered after infection as they cannot mimic the complex placental architecture and neglect the activity of resident immune cells. These drawbacks could be solved using placental explants, broadly employed in human medicine, and able to preserve its cellular architecture and function. Despite the availability of such materials is constrained by their short shelf-life, the development of adequate cryopreservation protocols could expand their use for research purposes. Herein, we review and discuss existing (and potential) in vivo, in vitro, and ex vivo ruminant placental models that have proven useful to unravel the pathogenic mechanisms and the host immune responses responsible for fetal death (or protection) caused by neosporosis and toxoplasmosis.

The interaction of classical complement component C1 with parasite and host calreticulin mediates Trypanosoma cruzi infection of human placenta

Background

9 million people are infected with Trypanosoma cruzi in Latin America, plus more than 300,000 in the United States, Canada, Europe, Australia, and Japan. Approximately 30% of infected individuals develop circulatory or digestive pathology. While in underdeveloped countries transmission is mainly through hematophagous arthropods, transplacental infection prevails in developed ones.

Methodology/Principal Findings

During infection, T. cruzi calreticulin (TcCRT) translocates from the endoplasmic reticulum to the area of flagellum emergence. There, TcCRT acts as virulence factor since it binds maternal classical complement component C1q that recognizes human calreticulin (HuCRT) in placenta, with increased parasite infectivity. As measured ex vivo by quantitative PCR in human placenta chorionic villi explants (HPCVE) (the closest available correlate of human congenital T. cruzi infection), C1q mediated up to a 3–5-fold increase in parasite load. Because anti-TcCRT and anti-HuCRT F(ab′)₂ antibody fragments are devoid of their Fc-dependent capacity to recruit C1q, they reverted the C1q-mediated increase in parasite load by respectively preventing its interaction with cell-bound CRTs from both parasite and HPCVE origins. The use of competing fluid-phase recombinant HuCRT and F(ab′)₂ antibody fragments anti-TcCRT corroborated this. These results are consistent with a high expression of fetal CRT on placental free chorionic villi. Increased C1q-mediated infection is paralleled by placental tissue damage, as evidenced by histopathology, a damage that is ameliorated by anti-TcCRT F(ab′)₂ antibody fragments or fluid-phase HuCRT.

Conclusions/Significance

T. cruzi infection of HPCVE is importantly mediated by human and parasite CRTs and C1q. Most likely, C1q bridges CRT on the parasite surface with its receptor orthologue on human placental cells, thus facilitating the first encounter between the parasite and the fetal derived placental tissue. The results presented here have several potential translational medicine aspects, specifically related with the capacity of antibody fragments to inhibit the C1q/CRT interactions and thus T. cruzi infectivity.

The Trypanosoma cruzi protozoan infects 9 million people in Latin America and increasing numbers in North America, Europe, Australia, and Japan. It is an important neglected parasitic disease in the Americas with no safe treatment available. One third of those infected develops incapacitating pathology. While in poor countries transmission of the parasite is mainly through blood feeding insects, transplacental infection is increasingly important in developed regions. Herein we show that T. cruzi calreticulin (TcCRT), a multifunctional protein, exteriorized by the parasite, mediates infection of human placenta, since it binds human complement component C1, a “danger signal” detector. (Complement is an innate immune defense system, with more than 40 plasma or membrane-bound proteins). However, in a parasite strategy, maternal C1 is utilized to infect placenta. Fetal calreticulin (HuCRT) is also easily detectable in placental tissues that are in direct contact with maternal blood. Thus, C1q by bridging parasite and HuCRT mediates high increases in cultured placental tissue infection with damaging consequences. Complete reversion of C1-mediated infection and a decreased placental damage, is observed in the presence of anti-TcCRT and anti-HuCRT antibody fragments, or fluid-phase competing HuCRT. It remains to be determined whether these mechanisms also operate in other intracellular protozoa.

In Vitro Infection of Trypanosoma cruzi Causes Decrease in Glucose Transporter Protein-1 (GLUT1) Expression in Explants of Human Placental Villi Cultured under Normal and High Glucose Concentrations

Trypanosoma cruzi, the etiologic Chagas' disease agent, induces changes in protein pattern of the human placenta syncytiotrophoblast. The glucose transporter protein-1 (GLUT1) is the primary isoform involved in transplacental glucose transport. We carried out in vitro assays to determine if T. cruzi infection would induce changes in placental GLUT1 protein expression under normal and high concentration of glucose. Using Western blot and immunohistological techniques, GLUT1 expression was determined in normal placental villi cultured under normal or high concentrations of glucose, with or without in vitro T. cruzi infection, for 24 and 48 hours. High glucose media or T. cruzi infection alone reduced GLUT1 expression. A yet more accentuated reduction was observed when infection and high glucose condition took place together. We inform, for the first time, that T. cruzi infection may induce reduction of GLUT1 expression under normal and high glucose concentrations, and this effect is synergic to high glucose concentrations.

Trypanosoma cruzi (Chagas' disease agent) reduces HIV-1 replication in human placenta

Background

Several factors determine the risk of HIV mother-to-child transmission (MTCT), such as coinfections in placentas from HIV-1 positive mothers with other pathogens. Chagas' disease is one of the most endemic zoonoses in Latin America, caused by the protozoan Trypanosoma cruzi. The purpose of the study was to determine whether T. cruzi modifies HIV infection of the placenta at the tissue or cellular level.

Results

Simple and double infections were carried out on a placental histoculture system (chorionic villi isolated from term placentas from HIV and Chagas negative mothers) and on the choriocarcinoma BeWo cell line. Trypomastigotes of T. cruzi (VD lethal strain), either purified from mouse blood or from Vero cell cultures, 24 h-supernatants of blood and cellular trypomastigotes, and the VSV-G pseudotyped HIV-1 reporter virus were used for the coinfections. Viral transduction was evaluated by quantification of luciferase activity. Coinfection with whole trypomastigotes, either from mouse blood or from cell cultures, decreased viral pseudotype luciferase activity in placental histocultures. Similar results were obtained from BeWo cells. Supernatants of stimulated histocultures were used for the simultaneous determination of 29 cytokines and chemokines with the Luminex technology. In histocultures infected with trypomastigotes, as well as in coinfected tissues, IL-6, IL-8, IP-10 and MCP-1 production was significantly lower than in controls or HIV-1 transducted tissue. A similar decrease was observed in histocultures treated with 24 h-supernatants of blood trypomastigotes, but not in coinfected tissues.

Conclusion

Our results demonstrated that the presence of an intracellular pathogen, such as T. cruzi, is able to impair HIV-1 transduction in an in vitro system of human placental histoculture. Direct effects of the parasite on cellular structures as well as on cellular/viral proteins essential for HIV-1 replication might influence viral transduction in this model. Nonetheless, additional mechanisms including modulation of cytokines/chemokines at placental level could not be excluded in the inhibition observed. Further experiments need to be conducted in order to elucidate the mechanism(s) involved in this phenomenon. Therefore, coinfection with T. cruzi may have a deleterious effect on HIV-1 transduction and thus could play an important role in viral outcome at the placental level.

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.

Molecular basis of mammalian cell invasion by Trypanosoma cruzi

Establishment of infection by Trypanosoma cruzi, the agent of Chagas' disease, depends on a series of events involving interactions of diverse parasite molecules with host components. Here we focus on the mechanisms of target cell invasion by metacyclic trypomastigotes (MT) and mammalian tissue culture trypomastigotes (TCT). During MT or TCT internalization, signal transduction pathways are activated both in the parasite and the target cell, leading to Ca2+ mobilization. For cell adhesion, MT engage surface glycoproteins, such as gp82 and gp35/50, which are Ca2+ signal-inducing molecules. In T. cruzi isolates that enter host cells in gp82-mediated manner, parasite protein tyrosine kinase as well as phospholipase C are activated, and Ca2+ is released from I P3-sensitive stores, whereas in T. cruzi isolates that attach to target cells mainly through gp35/50, the signaling pathway involving adenylate cyclase appears to be stimulated, with Ca2+ release from acidocalciosomes. In addition, T. cruzi isolate-dependent inhibitory signals, mediated by MT-specific gp90, may be triggered both in the host cell and the parasite. The repertoire of TCT molecules implicated in cell invasion includes surface glycoproteins of gp85 family, with members containing binding sites for laminin and cytokeratin 18, enzymes such as cruzipain, trans-sialidase, and an oligopeptidase B that generates a Ca2+-agonist from a precursor molecule.

Placental alkaline phosphatase (PLAP) study in diabetic human placental villi infected with Trypanosoma cruzi

Previous work has demonstrated that PLAP activity decreases in serum and placental villi from term chagasic and diabetic pregnant women. In vitro, T. cruzi induces changes in human syncytiotrophoblast's PLAP. Our aim was to determine if infection with T. cruzi induces changes in PLAP activity in diabetic and chagasic women's placenta, in order to elucidate if PLAP plays a role in the mechanisms of interaction between placenta and T. cruzi, and whether hyperglycemic conditions could worsen the placental infection. Using zymogrammes, Western blot, biochemical and immunohistological techniques, PLAP activity was determined in placental villi from diabetic and chagasic women, and in normal placentas cultured under hyperglycemic conditions with or without trypomastigotes. A significant reduction of PLAP expression was immunologically detected in infected diabetic and normal placental villi cultured under hyperglycemic conditions of 71 and 81%, respectively, compared with controls. A significant decrease of PLAP specific activity was registered in homogenates and in the culture media from both infected diabetic and normal placentas under hyperglycemic conditions (of about 50-70%), and in chagasic ones (of about 87%), when compared with controls. Thus, PLAP might be involved in parasite invasion and diabetic and hyperglycemic placentas could be more susceptible to T. cruzi infection.

Epidermal Growth Factor (EGF) in the Human Placental Infection with Trypanosoma cruzi

Maternal infection of Trypanosoma cruzi is associated with premature births, abortions and placentitis. A decrease in EGF levels has been suggested to occur in animals infected by T. cruzi, but there is no research about the levels of EGF in human patients with Chagas' disease. We evaluated serum EGF levels in pregnant women with and without the disease, and with immunological methods detected EGF receptors and EGF in both groups of placentae and in cultures of normal placental villi with and without parasites. PLAP in placentae from those women was also immunologically detected, since EGF can induce the release of PLAP from the trophoblast surface and PLAP is suggested to be a receptor allowing parasite invasion of the placenta. Plasma from women with Chagas' disease contained lower level of EGF when compared to plasma of healthy women. Placentae from women with Chagas' disease showed lower PLAP expression but same level of detectable EGF receptors and EGF when compared with placentae from women without the disease. Culture with parasites did not reduce EGFr level. Results suggest a lower availability of EGF in women with Chagas' disease, which could explain several malfunctions of the placenta associated with maternal Chagas' disease.

Role of placental alkaline phosphatase in the internalization of trypomatigotes of Trypanosoma cruzi into HEp2 cells

BACKGROUND

In vitro, Trypanosoma cruzi invades a wide variety of mammalian cells by an unique process that is still poorly understood. Trypomastigotes adhere to specific receptors on the outer membrane of host cells before intracellular invasion, causing calcium ion mobilization and rearrangement of host cell microfilaments.

OBJECTIVE

To test if placental alkaline phosphatase (PLAP), a trophoblast plasma membrane protein anchored by a glycosylphosphatidylinositol molecule, is involved in the transplacental transmission of this parasite.

METHOD

We cultured HEp2 cells with the parasite and studied PLAP and actin microfilaments. The results were correlated with invasion rate.

RESULTS

Human HEp2 tumour cells express PLAP. HEp2 cells infected with trypomastigotes showed alteration in their alkaline phosphatase activity and a different pattern of actin organization, compared to control cells. Perturbation of PLAP from HEp2 cells before infection with T. cruzi trypomastigotes decreased the invasion rate.

CONCLUSION

Placental alkaline phosphatase could be involved in the internalization of T. cruzi into HEp2 cells, via activation of tyrosine kinase and rearrangement of actin microfilaments.