Integrin-dependent Migratory Switches Regulate the Translocation of Toxoplasma-infected Dendritic Cells Across Brain Endothelial Monolayers

Abstract

Multiple cellular processes, such as immune responses and cancer cell metastasis, crucially depend on the interconversion between distinct migratory states. However, knowledge is scarce on how infectious agents impact the processes of cell migration at restrictive biological barriers. In extracellular matrix, dendritic cells (DCs) infected by the obligate intracellular protozoan Toxoplasma gondii undergo mesenchymal-to-amoeboid transition (MAT) for rapid integrin-independent migration. Here, in a cellular model of the blood-brain barrier, we report that parasitised DCs shift to integrin-dependent motility and adhesion on polarised endothelium, accompanied by elevated transendothelial migration (TEM). Upon contact with endothelium, parasitised DCs dramatically reduced velocities and adhered under both static and shear stress conditions, thereby obliterating the infection-induced amoeboid motility displayed in collagen matrix. The motility of adherentparasitised DCs on endothelial monolayers was restored by blockade of β1 and β2 integrins or ICAM-1, which conversely reduced motility on collagen-coated surfaces. Moreover, parasitised DCs exhibited enhanced translocation across highly polarised primary murine brain endothelial cell monolayers. Blockade of β1, β2 integrins, ICAM-1 and PECAM-1 reduced TEM frequencies. Finally, gene silencing of the pan-integrin-cytoskeleton linker talin ( Tln1 ) or of β1 integrin ( Itgb1 ) in primary DCs resulted in increased motility on endothelium and decreased TEM. Adding to the paradigms of leukocyte diapedesis, the findings provide novel insights in how an intracellular pathogen modulates the migratory properties of leukocytes in response to the cellular environment, to promote infection-related dissemination.