Yihong Cai

STAT3-dependent transactivation of miRNA genes following Toxoplasma gondii infection in macrophage

BackgroundThe apicomplexan parasite Toxoplasma gondii can infect and replicate in virtually any nucleated cell in many species of warm-blooded animals; T. gondii has elaborate mechanisms to counteract host-cell apoptosis in order to maintain survival and breed in the host cells.MethodsUsing microarray profiling and a combination of conventional molecular approaches, we investigated the levels of microRNAs (miRNAs ) in human macrophage during T. gondii infection. We used molecular tools to examine Toxoplasma-upregualted miRNAs to revealed potential signal transducers and activators of transcription 3(STAT3) binding sites in the promoter elements of a subset of miRNA genes. We analysed the apoptosis of human macrophage with the functional inhibition of the STAT3-binding miRNAs by flow cytometry.ResultsOur results demonstrated differential alterations in the mature miRNA expression profile in human macrophage following T. gondii infection. Database analysis of Toxoplasma-upregulated miRNAs revealed potential STAT3 binding sites in the promoter elements of a subset of miRNA genes. We demonstrated that miR-30c-1, miR-125b-2, miR-23b-27b-24-1 and miR-17 ~ 92 cluster genes were transactivated through promoter binding of the STAT3 following T. gondii infection. Importantly, functional inhibition of selected STAT3-binding miRNAs in human macropahges increased apoptosis of host cells.ConclusionsA panel of miRNAs is regulated through promoter binding of the STAT3 in human macrophage and these miRNAs are involved in anti-apoptosis in response to T. gondii infection.

Activated microglia contribute to neuronal apoptosis in Toxoplasmic encephalitis

BackgroundA plethora of evidence shows that activated microglia play a critical role in the pathogenesis of the central nervous system (CNS). Toxoplasmic encephalitis (TE) frequently occurs in HIV/AIDS patients. However, knowledge remains limited on the contributions of activated microglia to the pathogenesis of TE.MethodsA murine model of reactivated encephalitis was generated in a latent infection with Toxoplasma gondii induced by cyclophosphamide. The neuronal apoptosis in the CNS and the profile of pro-inflammatory cytokines were assayed in both in vitro and in vivo experiments.ResultsMicroglial cells were found to be activated in the cortex and hippocampus in the brain tissues of mice. The in vivo expression of interleukin-6 (IL-6), interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and inducible nitric oxide synthase (iNOS) were up-regulated in TE mice, and accordingly, the neuronal apoptosis was significantly increased. The results were positively correlated with those of the in vitro experiments. Additionally,apoptosis of the mouse neuroblastoma type Neuro2a (N2a) remarkably increased when the N2a was co-cultured in transwell with microglial cells and Toxoplasma tachyzoites. Both in vivo and in vitro experiments showed that minocycline (a microglia inhibitor) treatment notably reduced microglial activation and neuronal apoptosis.ConclusionsActivated microglia contribute to neuronal apoptosis in TE and inhibition of microglia activation might represent a novel therapeutic strategy of TE.

Trophoblast apoptosis through polarization of macrophages induced by Chinese Toxoplasma gondii isolates with different virulence in pregnant mice

Toxoplasma gondii is an apicomplexan parasite capable of transplacental transmission to cause spontaneous abortion or significant disease in the surviving neonate. Different from the dominant genotypes of T. gondii strains in European and North American which belong to three distinct clonal lineages, type I, type II, and type III, isolates from China possess the predominant genotype of China 1(ToxoDB#9) with a different virulence. The genotype-associated pathogenesis has been investigated previously. Based on two isolates of T. gondii from Chinese wild cats, a murine model of pregnancy and one transwell system in vitro, here we reported differentially polarized activation of macrophages induced by genotype China 1 strains, TgCtwh3 and TgCtwh6 with different virulence to mice, and its impact on trophoblast apoptosis. The results showed that macrophages were alternatively activated when infected with virulent TgCtwh3 while classically activated when infected with low virulent (cyst-forming) TgCtwh6 both in vitro and in vivo. By the analysis of flow cytometry, the percentage of the Th1 cells in two infection groups decreased significantly, and the Th2 cells from spleen escalated only in the virulent TgCtwh3 group. Interestingly, the high parasite burden was noted in the placenta of TgCtwh3-infected group whereas the inflammatory cells infiltration predominates in the TgCtwh6-infected group. In vivo trophoblast apoptosis in TgCtwh3 group was found to be more obvious when compared with TgCtwh6 although it was present in both. The present observations indicate that polarization of macrophages and modulation of Th subsets induced by the isolates with identical genotype but different virulence could contribute to trophoblast apoptosis through different mechanisms, suggesting a virulence-associated pathogenesis of T. gondii in abnormal pregnant outcome.

Polarization of macrophages induced by Toxoplasma gondii and its impact on abnormal pregnancy in rats.

Toxoplasma gondii infection is the leading cause of fetal intrauterine growth retardation among the five kinds of pathogens termed as TORCH, including Toxoplasma, Rubella virus, Cytomegalo virus, herpes virus and others during pregnancy. Pathogens infect the fetus through the placenta. T. gondii infection may result in congenital toxoplasmosis, miscarriage, stillbirth, and preemie, and increase pregnancy complications. Adaptive immune response induced by T. gondii infection stimulates T cells and macrophages to produce high levels of cytokines. Physiologically, the microenvironment of pregnancy was Th2-dominant. Here we set up a pregnant Sprague-Dawley rat model, and reported the polarization of macrophages induced by genotype Chinese 1 strain (Wh6) of Toxoplasma, and its adverse impact on pregnancy. The results showed that Wh6 infection pre- or in-gestation both led to abnormal pregnancy outcomes. Peritoneal macrophages in pre-gestation infection were polarized toward classically activated macrophages (M1), while in-gestation infection drove macrophages to polarize toward M2 activation. The Th2-dominant immune response in pregnant rat somewhat inhibits the excessive bias of the macrophages toward M1, and partially, toward M2. Infection of pre- and in-gestation may alter the physiological immune microenvironment in pregnant rats, giving rise to abnormal pregnancy outcomes.

Comparative studies of macrophage-biased responses in mice to infection with Toxoplasma gondii ToxoDB #9 strains of different virulence isolated from China

BackgroundDifferent from three clonal lineages of Toxoplasma gondii in North America and Europe, the genotype China 1 is predominantly prevalent in China. However, there are different virulent isolates within China 1, such as virulent TgCtwh3 and avirulent TgCtwh6, and little is known about differences in macrophage activation between them. The objective of this study focused on cytokine production, phenotype and markers of activated macrophages, and correlated signaling pathway induced by the two isolates.MethodsAdherent peritoneal macrophages (termed Wh3-Mφ and Wh6-Mφ, respectively) harvested from infected mice were cultured for detection of Nitric Oxide and arginase activity, and activated markers on Wh3-Mφ/Wh6-Mφ were determined by flow cytometry. In in vitro experiments, the levels of IL-12p40 and TNF-α were measured using ELISA kits, and mRNA expressions of IL-12p40, TNF-α, iNOS, Arg-1 and Ym1 were assayed by real-time PCR. To confirm the activation state of NF-kB p65 in infected cells stained by IF, protein levels of iNOS, Arg-1, Ym1, nuclear NF-κB p65, and phosphorylation of STAT6/STAT3/IκBα were evaluated by Western Blotting. A one-way ANOVA test was used to compare differences among multiple groups.ResultsThe result revealed that contrary to the virulent TgCtwh3, the less virulent TgCtwh6 isolate induced a significant increase in IL-12p40 and TNF-α. Although both isolates down-regulated CD80, CD86 and MHCII molecule expression on macrophages, TgCtwh3 promoted up-regulation of PD-L2 and CD206. Wh6-Mφ generated a high level of NO whereas Wh3-Mφ up-regulated Ym1 and arginase expression at transcriptional and protein levels. In terms of signaling pathway, TgCtwh3 induced phospho-STAT6, conversely, TgCtWh6 led to NF-κB p65 activation.ConclusionsThe virulent TgCtwh3 isolate induced macrophages to polarize toward alternatively activated cells with STAT6 phosphorylation, whereas the less virulent TgCtwh6 elicited the development of classically activated macrophages with nuclear translocation of NF-κB p65. This discrepancy suggests that it is necessary to thoroughly analyze the genotype of TgCtwh3 and TgCtwh6, and to further study other effector molecules that contribute to the macrophage polarization in T. gondii.

rROP2186–533: A Novel Peptide Antigen for Detection of IgM Antibodies Against Toxoplasma gondii

Toxoplasma gondii infections are prevalent in a wide range of mammalian hosts including humans. Infection in pregnant women may cause the transmission of parasite to the fetus that makes serious problems. IgM antibodies against Toxoplasma (Toxo-IgM) have been believed to be significant indicators for both recently acquired and congenital toxoplasmosis. So far, however, there has not been any recognized protein of T. gondii that specifically reacts to IgM antibodies. Here, an antigen exclusively for detection of IgM antibodies screened by two-dimensional electrophoresis and mass spectrometry has been reported. The study identified 13 Toxoplasma proteins probed by IgG antibodies and one (rhpotry protein 2 [ROP2]) by IgM antibodies with human sera of Toxo-IgM(-)-IgG(+) and -IgM(+)-IgG(-), respectively, which had been prescreened by Toxo-IgM and -IgG commercial kits from the suspected cases. Following cloning, expression, and purification of the fragment of ROP2(186-533), an enzyme-linked immunosorbent assay with rROP2(186-533) to measure IgM and IgG antibodies was developed. As a result, 100%(48/48) of sera with Toxo-IgM(+)-IgG(-)showed positive Toxo-IgM but none of them (0%) showed positive Toxo-IgG when rROP2(186-533) was used as antigen. Neither Toxo-IgG nor Toxo-IgM antibodies were found when tested with 59 sera of Toxo-IgM(-)-IgG(+). These results indicate that rROP2(186-533) could be used as an antigen that specifically capture Toxo-IgM antibodies and may have a high potential in the serological diagnosis of both acute acquired and congenital toxoplasmosis.

Macrophages Polarized by Expression of ToxoGRA15II Inhibit Growth of Hepatic Carcinoma

A growing body of evidence suggests that tumor-associated macrophages are deeply involved in the hepatocellular carcinoma proliferation and account for the large proportion of infiltrated cells in tumor tissues and play a major role in promotion of tumor growth. On the other hand, studies have demonstrated that Toxoplasma gondii virulence-associated molecule of dense granule protein (ToxoGRA15II) tends to induce classically activated macrophages (M1) differentiation. Thus, we explored the M1 induced by ToxoGRA15II in vitro and its inhibitory impact on the proliferation, invasion, and metastasis of hepatic carcinoma in murine model. Here, we constructed recombinant plasmid of pegfp-gra15II and subsequently ligate it to lentivirus (Lv) vector, with which RAW264.7 was transfected. The results showed that the transfected macrophages were polarized to M1. Coculture of the M1 with Hepa1-6 cells showed a remarkable inhibition of migration and invasion of the tumor cells and decreased expressions of matrix metalloproteinase (MMP)-9 and MMP-2 without notable apoptosis of Hepa1-6 cells. Subsequently, ToxoGRA15II-polarized macrophages inoculated to tumor-bearing C57BL/6 mice were seen in both spleen and tumor tissues, and tumor growth was sharply restricted. Particularly, interleukin-6 (IL-6) expression, which is closely associated with the cancer malignant behaviors, was significantly dampened in tumor tissues. In addition, expression of TNF-α and IL-12 mRNAs was increased, whereas IL-6 and interleukin-10 mRNAs were downregulated in splenocytes. Our results indicate that the effector molecule of ToxoGRA15II may induce macrophage polarization to M1 that has a restrictive effect on tumor growth via its related cytokines profile in tumor and spleen tissues. Besides, ToxoGRA15II, due to its early activation of specified cell population and non-toxicity to mammalians, has a potential value for a novel therapeutic strategy of enhancing host innate immunity against tumor development.

Toxoplasma gondii inhibits differentiation of C17.2 neural stem cells through Wnt/β-catenin signaling pathway.

Toxoplasma gondii is a major cause of congenital brain disease. T. gondii infection in the developing fetus frequently results in major neural developmental damage; however, the effects of the parasite infection on the neural stem cells, the key players in fetal brain development, still remain elusive. This study is aiming to explore the role of T. gondii infection on differentiation of neural stem cells (NSCs) and elucidate the underlying molecular mechanisms that regulate the inhibited differentiation of NSCs induced by the infection. Using a differentiation medium, i.e. , DMEM: F12 (1:1 mixture) supplemented with 2% N2, C17.2 neural stem cells (NSCs) were able to differentiate to neurons and astrocytes, respectively evidenced by immunofluorescence staining of differentiation markers including βIII-tubulin and glial fibrillary acidic protein (GFAP). After 5-day culture in the differentiation medium, the excreted-secreted antigens of T. gondii (Tg-ESAs) significantly down-regulated the protein levels of βIII-tubulin and GFAP in C17.2 NSCs in a dose-dependent manner. The protein level of β-catenin in the nucleus of C17.2 cells treated with both wnt3a (a key activator for Wnt/β-catenin signaling pathway) and Tg-ESAs was significantly lower than that in the cells treated with only wnt3a, but significantly higher than that in the cells treated with only Tg-ESAs. In conclusion, the ESAs of T. gondii RH blocked the differentiation of C17.2 NCSs and downregulated the expression of β-catenin, an essential component of Wnt/β-catenin signaling pathway. The findings suggest a new mechanism underlying the neuropathogenesis induced by T. gondii infection, i.e. inhibition of the differentiation of NSCs via blockade of Wnt/β-catenin signaling pathway, such as downregulation of β-catenin expression by the parasite ESAs.

Genotype-Associated Arginase 1 Expression in Rat Peritoneal Macrophages Induced by Toxoplasma gondii

Abstract:  Toxoplasma gondii induces polarization of mouse macrophages, including both classically activated macrophages (M1) and alternatively activated macrophages (M2) in a genotype-related manner. Here we present a novel result that the Wh6 strain with type Chinese 1, which is predominantly prevalent in China, induces Arg1 expression in a STAT6-dependent manner in primary rat peritoneal macrophages as compared to the PRU stain with type II, which elicited a high expression of Arg1 in a C/EBPβ-dependent manner. In addition, dexamethasone inhibited Arg1 expression in rat macrophages in both treatments. Our data suggest that Arg1 expression, which is abundant in polarized M2 cells, is associated with strain/genotype differences from different pathways.

A mechanistic study of Toxoplasma gondii ROP18 inhibiting differentiation of C17.2 neural stem cells

BackgroundCongenital infection of Toxoplasma gondii is an important factor causing birth defects. The neural stem cells (NSCs) are found to be one of the target cells for the parasite during development of the brain. As a key virulence factor of the parasite that hijacks host cellular functions, ROP18 has been demonstrated to mediate the inhibition of host innate and adaptive immune responses through specific binding different host immunity related molecules. However, its pathogenic actions in NSCs remain elusive.ResultsIn the present study, ROP18 recombinant adenovirus (Ad-ROP18) was constructed and used to infect C17.2 NSCs. After 3d- or 5d–culture in differentiation medium, the differentiation of C17.2 NSCs and the activity of the Wnt/β-catenin signaling pathway were detected. The results showed that the protein level of βIII-tubulin, a marker of neurons, in the Ad-ROP18-transfected C17.2 NSCs was significantly decreased, indicating that the differentiation of C17.2 NSCs was inhibited by the ROP18. The β-catenin level in the Ad-ROP18-transfected C17.2 NSCs was found to be lower than that in the Ad group. Also, neurogenin1 (Ngn1) and neurogenin2 (Ngn2) were downregulated significantly (P < 0.05) in the Ad-ROP18-transfected C17.2 NSCs compared to the Ad group. Accordingly, the TOP flash/FOP flash dual-luciferase report system showed that the transfection of Ad-ROP18 decreased the Wnt/β-catenin pathway activity in the C17.2 NSCs.ConclusionsThe inhibition effect of the ROP18 from T. gondii (TgROP18) on the neuronal differentiation of C17.2 NSCs was at least partly mediated through inhibiting the activity of the Wnt/β-catenin signaling pathway, eventually resulting in the downregulation of Ngn1 and Ngn2. The findings help to better understand potential mechanisms of brain pathology induced by TgROP18.