1. |
- Kanatani, Sachie, et al.
(författare)
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Voltage-dependent calcium channel signaling mediates GABA(A) receptor-induced migratory activation of dendritic cells infected by Toxoplasma gondii
- 2017
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Ingår i: PLoS Pathogens. - : Public Library of Science (PLoS). - 1553-7366 .- 1553-7374. ; 13:12
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Tidskriftsartikel (refereegranskat)abstract
- The obligate intracellular parasite Toxoplasma gondii exploits cells of the immune system to disseminate. Upon T. gondii-infection,. Upsilon-aminobutyric acid (GABA)/GABAA receptor signaling triggers a hypermigratory phenotype in dendritic cells (DCs) by unknown signal transduction pathways. Here, we demonstrate that calcium (Ca2+) signaling in DCs is indispensable for T. gondii-induced DC hypermotility and transmigration in vitro. We report that activation of GABAA receptors by GABA induces transient Ca2+ entry in DCs. Murine bone marrow-derived DCs preferentially expressed the L-type voltage-dependent Ca2+ channel (VDCC) subtype Cav1.3. Silencing of Cav1.3 by short hairpin RNA or selective pharmacological antagonism of VDCCs abolished the Toxoplasma-induced hypermigratory phenotype. In a mouse model of toxoplasmosis, VDCC inhibition of adoptively transferred Toxoplasma-infected DCs delayed the appearance of cell-associated parasites in the blood circulation and reduced parasite dissemination to target organs. The present data establish that T. gondii-induced hypermigration of DCs requires signaling via VDCCs and that Ca2+ acts as a second messenger to GABAergic signaling via the VDCC Cav1.3. The findings define a novel motility-related signaling axis in DCs and unveil that interneurons and DCs share common GABAergic motogenic pathways. T. gondii employs GABAergic non-canonical pathways to induce host cell migration and facilitate dissemination.
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2. |
- Sultana, M. Afifa, et al.
(författare)
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Downmodulation of Effector Functions in NK Cells upon Toxoplasma gondii Infection
- 2017
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Ingår i: Infection and Immunity. - 0019-9567 .- 1098-5522. ; 85:10
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Tidskriftsartikel (refereegranskat)abstract
- The obligate intracellular parasite Toxoplasma gondii can actively infect any nucleated cell type, including cells from the immune system. The rapid transfer of T. gondii from infected dendritic cells to effector natural killer (NK) cells may contribute to the parasite's sequestration and shielding from immune recognition shortly after infection. However, subversion of NK cell functions, such as cytotoxicity or production of proinflammatory cytokines, such as gamma interferon (IFN-γ), upon parasite infection might also be beneficial to the parasite. In the present study, we investigated the effects of T. gondii infection on NK cells. In vitro, infected NK cells were found to be poor at killing target cells and had reduced levels of IFN-γ production. This could be attributed in part to the inability of infected cells to form conjugates with their target cells. However, even upon NK1.1 cross-linking of NK cells, the infected NK cells also exhibited poor degranulation and IFN-γ production. Similarly, NK cells infected in vivo were also poor at killing target cells and producing IFN-γ. Increased levels of transforming growth factor β production, as well as increased levels of expression of SHP-1 in the cytosol of infected NK cells upon infection, were observed in infected NK cells. However, the phosphorylation of STAT4 was not altered in infected NK cells, suggesting that transcriptional regulation mediates the reduced IFN-γ production, which was confirmed by quantitative PCR. These data suggest that infection of NK cells by T. gondii impairs NK cell recognition of target cells and cytokine release, two mechanisms that independently could enhance T. gondii survival.
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3. |
- Fuks, Jonas
(författare)
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Host molecular determinants of toxoplasma gondii dissemination
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Humans and animals acquire the parasite Toxoplasma gondii through contaminated food or water, upon which the parasite rapidly disseminates in the host. In immunocompetent individuals, this acute phase is transient and leads to chronic colonization of preferentially the central nervous system (CNS). The latent chronic infection may reactivate in immunocompromised individuals, causing potentially lethal encephalitis. It has been established that dendritic cells (DCs) are exploited by T. gondii as “Trojan horses” to facilitate dissemination in the host. T. gondii infected DCs exhibit a hypermigratory phenotype that is a major determinant for enhanced dissemination of the parasite. The host cell pathways involved in the onset and maintenance of this phenotype are largely unknown. This thesis has investigated potential mechanisms of host cell subversion, addressing dissemination during the acute phase of infection and reactivated infection in the brain upon immunosuppression. The main findings of the thesis are listed below. Significant CD8+ T cell infiltration and activation of CNS resident microglia and astrocytes was observed in close vicinity of reactivated T. gondii foci in mouse brain. Cortical microglia exhibited hypermigration upon T. gondii infection in vitro, as previously shown for DCs. Infected microglia and astrocytes showed increased sensitivity to T cell mediated killing, allowing parasite transmission to surrounding cells. Thus, resident and infiltrating cells may act as Trojan horses, potentiating local T. gondii dissemination in the encephalitic brain. We developed a motility assay in which cells are tracked while migrating in a collagen matrix. In this assay, T. gondii infected DCs displayed increased velocities as early as 10 min post invasion. This “hypermotility” coincided with the redistribution of actin and integrins. Infected DCs also chemotaxed along a gradient of CCR7 ligand CCL19. Collectively, this series of cellular events contributes to a shift in the migratory capacity of T. gondii infected DCs, expanding the concept of the hypermigratory phenotype. We showed that DCs express functional γ-aminobutyric acid (GABA) receptors and are capable of producing and secreting GABA. T. gondii infection enhanced GABA secretion, while inhibition of GABA production, transport or GABA receptors abolished the hypermigratory phenotype. This autocrine GABAergic activation was crucial for DCs to act as Trojan horses in T. gondii dissemination in vivo. This thesis describes the expression of the voltage dependent Ca2+ channel CaV1.3 in murine DCs. We found that GABAergic activation was linked to CaV1.3 and that selective blockade or knockdown of the latter abolished T. gondii induced hypermotility in DCs. This fast- acting signaling axis may allow rapid parasite manipulation of host cell migration. In summary, we have shown that T. gondii exploits non-canonical migration-related host signaling pathways to enhance its dissemination. Several cell types are likely involved as Trojan horses at different stages of the infection process, e.g. DCs, T cells and microglia. This work also illustrates that the study of parasite-host interactions may further our understanding of basic cellular mechanisms, such as motility, and uncover novel signaling pathways in the host.
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4. |
- Weidner, Jessica M., et al.
(författare)
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Rapid cytoskeleton remodelling in dendritic cells following invasion by Toxoplasma gondii coincides with the onset of a hypermigratory phenotype
- 2013
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Ingår i: Cellular Microbiology. - : Hindawi Limited. - 1462-5814 .- 1462-5822. ; 15:10, s. 1735-1752
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Tidskriftsartikel (refereegranskat)abstract
- Host cell manipulation is an important feature of the obligate intracellular parasite Toxoplasma gondii. Recent reports have shown that the tachyzoite stages subvert dendritic cells (DC) as a conduit for dissemination (Trojan horse) during acute infection. To examine the cellular basis of these processes, we performed a detailed analysis of the early events following tachyzoite invasion of human monocyte-derived DC. We demonstrate that within minutes after tachyzoite penetration, profound morphological changes take place in DC that coincide with a migratory activation. Active parasite invasion of DC led to cytoskeletal actin redistribution with loss of adhesive podosome structures and redistribution of integrins (CD18 and CD11c), that concurred with the onset of DC hypermotility in vitro. Inhibition of parasite rhoptry secretion and invasion, but not inhibition of parasite or host cell protein synthesis, abrogated the onset of morphological changes and hypermotility in DC dose-dependently. Also, infected DC, but not by-stander DC, exhibited upregulation of C-C chemokine receptor 7 (CCR7). Yet, the onset of parasite-induced DC hypermotility preceded chemotactic migratory responsesin vitro. Collectively, present data reveal that invasion of DC by T. gondii initiates a series of regulated events, including rapid cytoskeleton rearrangements, hypermotility and chemotaxis, that promote the migratory activation of DC.
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5. |
- Fuks, Jonas M, et al.
(författare)
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GABAergic Signaling Is Linked to a Hypermigratory Phenotype in Dendritic Cells Infected by Toxoplasma gondii
- 2012
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Ingår i: PLoS pathogens. - : Public Library of Science (PLoS). - 1553-7374. ; 8:12, s. e1003051-
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Tidskriftsartikel (refereegranskat)abstract
- During acute infection in human and animal hosts, the obligate intracellular protozoan Toxoplasma gondii infects a variety of cell types, including leukocytes. Poised to respond to invading pathogens, dendritic cells (DC) may also be exploited by T. gondii for spread in the infected host. Here, we report that human and mouse myeloid DC possess functional γ-aminobutyric acid (GABA) receptors and the machinery for GABA biosynthesis and secretion. Shortly after T. gondii infection (genotypes I, II and III), DC responded with enhanced GABA secretion in vitro. We demonstrate that GABA activates GABA(A) receptor-mediated currents in T. gondii-infected DC, which exhibit a hypermigratory phenotype. Inhibition of GABA synthesis, transportation or GABA(A) receptor blockade in T. gondii-infected DC resulted in impaired transmigration capacity, motility and chemotactic response to CCL19 in vitro. Moreover, exogenous GABA or supernatant from infected DC restored the migration of infected DC in vitro. In a mouse model of toxoplasmosis, adoptive transfer of infected DC pre-treated with GABAergic inhibitors reduced parasite dissemination and parasite loads in target organs, e.g. the central nervous system. Altogether, we provide evidence that GABAergic signaling modulates the migratory properties of DC and that T. gondii likely makes use of this pathway for dissemination. The findings unveil that GABA, the principal inhibitory neurotransmitter in the brain, has activation functions in the immune system that may be hijacked by intracellular pathogens.
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