Voltage-dependent calcium channel signaling mediates GABAA receptor-induced migratory activation of dendritic cells infected by Toxoplasma gondii.

Sachie Kanatani,Einar B Olafsson,Linda Westermark,Per Uhlén,Antonio Barragan,Jonas M Fuks,Manuel Varas-Godoy,Benedict Chambers,Eric Y Denkers

doi:10.1371/journal.ppat.1006739

Abstract

The obligate intracellular parasite Toxoplasma gondii exploits cells of the immune system to disseminate. Upon T. gondii-infection, γ–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.

Highlights

The obligate intracellular parasite Toxoplasma gondii chronically infects a large portion of the global human population and is capable of infecting any warm-blooded vertebrate [1]
Dendritic cells are considered the gatekeepers of the immune system but can, paradoxically, function as ‘Trojan horses’ to mediate dissemination of the common intracellular parasite Toxoplasma gondii
Calcium signaling in Toxoplasma-infected hypermigratory dendritic cells (DCs) study design, data collection and analysis, decision to publish, or preparation of the manuscript

Summary

Introduction

The obligate intracellular parasite Toxoplasma gondii chronically infects a large portion of the global human population and is capable of infecting any warm-blooded vertebrate [1]. Previous studies have demonstrated that active invasion of dendritic cells (DCs) by T. gondii tachyzoites rapidly (within minutes) induces a hypermigratory phenotype in parasitized DCs [3] This migratory activation is characterized by cytoskeletal rearrangements and dramatically enhanced cellular locomotion, termed hypermotility [4], and enhanced transmigratory activity in vitro [5]. The initiation of the hypermigratory phenotype in DCs is related to the discharge of secretory organelles during parasite invasion and does not depend on de novo protein synthesis in the host cell [4]. It is mediated through non-canonical GABAergic signaling pathways, and is independent of MyD88-mediated TLR signaling and chemotaxis [3,4,5, 8]

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