Cell surface vimentin is involved in matrix stiffness-dependent infection of endothelial cells by Listeria monocytogenes

Vascular endothelial cells (VECs) line the inner lumen of vessels forming a protective barrier against spread of bacterial infection from the bloodstream into underlying tissue. VECs display remarkable phenotypic heterogeneity in part due to the different mechanical stimuli transmitted from their extracellular environment. Although VEC response to mechanical signals has been studied extensively, how bacterial uptake occurs in VECs residing on substrates of varying stiffness has not been explored. We use Listeria monocytogenes , a facultative intracellular bacterial pathogen, to determine the biophysical relationships between the stiffness of the matrix underlying VECs and bacterial infection. We report that adhesion of L. monocytogenes to human microvascular endothelial cells (HMEC-1), and therefore subsequent infection of the host cells, increases monotonically with increasing matrix stiffness, an effect that requires the activity of focal adhesion kinase (FAK). We identified cell surface vimentin as a candidate surface receptor mediating stiffness-dependent adhesion of L. monocytogenes to HMEC-1 and found that bacterial infection of these host cells is inhibited when surface vimentin is blocked with an antibody or pharmacologically, or when vimentin expression is knocked down. Although the interaction between the host cell receptor Met and the bacterial virulence factor InlB contributes to invasion of HMEC-1 by L. monocytogenes , this interaction does not affect initial adhesion of bacteria to the host cell surface and is not sensitive to substrate stiffness. Our results identify a novel pathway wherein increased extracellular matrix stiffness sensed by VECs leads to enhanced FAK activity that augments the amount of vimentin exposed at the surface of VECs, that in turn increases adhesion and uptake of L. monocytogenes .