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 interconvertible migration modes. However, knowledge is scarce on how infectious agents impact the processes of cell adhesion and 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 adhere to polarised endothelium and shift to integrin-dependent motility, 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 adherent parasitised 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 impacts the migratory plasticity of leukocytes in response to the cellular environment, to promote infection-related dissemination.

Blood-brain barrier-restricted translocation of Toxoplasma gondii from cortical capillaries

“…Hypothetically, this together with the restricted diameter of capillaries may facilitate the adhesion, invasion and crossing of T. gondii tachyzoites. In vitro, ICAM-1 and integrins are implicated in adhesion and transmigration of T. gondii tachyzoites ( Barragan et al, 2005 ) and of parasitized leukocytes ( Ueno et al, 2014 ; Ross et al, 2021 ). Among other inflammatory parameters and cell adhesion molecules (CAMs), here we report elevated expression of ICAM-1 and VCAM-1 in infected brains and, specifically, in purified brain microvessels from challenged mice.…”

“…Yet, this does not rule out that single translocation events of T. gondii or egress of tachyzoites from single endothelial cells transiently destabilize the BBB below the detection threshold for the permeability tracer EB. In in vitro models using polarized primary brain endothelium, extracellular tachyzoites and parasitized dendritic cells rapidly translocated in absence of endothelial cell lysis, with a modest perturbation of the transcellular electrical resistance (TCER) but, importantly, in absence of leakage of a low-molecular weight permeability tracer ( Ross et al, 2019 ; Ross et al, 2021 ). In sharp contrast, cellular depolarization events or lysis of cells in the monolayers following parasite replication at later time-points led to significant decreases in TCER and dramatic elevations of permeability tracer concentration in vitro ( Ross et al, 2019 ; Ross et al, 2021 ).…”

Toxoplasma effector-induced ICAM-1 expression by infected dendritic cells potentiates transmigration across polarised endothelium

“…Motility assays were performed as previously described ( 24 ). Briefly, DCs were challenged with freshly egressed T. gondii tachyzoites (MOI 3) for 4 h (resulting in 70–80% infection frequency) and with soluble reagents as indicated.…”

“…We recently described an important role for leukocyte integrins and endothelial CAMs in the transmigration of T. gondii -challenged DCs across polarised monolayers of primary murine brain endothelium ( 24 ). However, while endothelial ICAM-1 is crucial for TEM ( 4 ), the implication of leukocyte ICAM-1 in diapedesis and, specifically, in TEM associated with microbial pathogenesis has remained unexplored ( 25 ).…”

Neuroimmunology of Common Parasitic Infections in Africa

“…Paracellular entry across endothelium implies passing cellular tight junctions (128)(129)(130)(131) while transcellular entry may occur after apical parasite invasion of the endothelium and basolateral exit after replication (132)(133)(134). Additionally, infected leukocytes, such as parasitized dendritic cells, may mediate transportation into the parenchyma (135)(136)(137).…”