Probing the biomechanical contribution of the endothelium to lymphocyte migration: diapedesis by the path of least resistance

Abstract

Immune cell trafficking requires the frequent breaching of the endothelial barrier either directly through individual cells ('transcellular' route) or through the inter-endothelial junctions ('paracellular' route). What determines the loci or route of breaching events is an open question with important implications for overall barrier regulation. We hypothesized that basic biomechanical properties of the endothelium might serve as crucial determinants of this process. By altering junctional integrity, cytoskeletal morphology and, consequently, local endothelial cell stiffness of different vascular beds, we could modify the preferred route of diapedesis. In particular, high barrier function was associated with predominantly transcellular migration, whereas negative modulation of junctional integrity resulted in a switch to paracellular diapedesis. Furthermore, we showed that lymphocytes dynamically probe the underlying endothelium by extending invadosome-like protrusions (ILPs) into its surface that deform the nuclear lamina, distort actin filaments and ultimately breach the barrier. Fluorescence imaging and pharmacologic depletion of F-actin demonstrated that lymphocyte barrier breaching efficiency was inversely correlated with local endothelial F-actin density and stiffness. Taken together, these data support the hypothesis that lymphocytes are guided by the mechanical 'path of least resistance' as they transverse the endothelium, a process we term 'tenertaxis'.

Molecular-Scale Biophysical Modulation of an Endothelial Membrane by Oxidized Phospholipids

“…Briefly, an increase in endothelial cell contractility through Rho mechanisms is recognized to play a major role in control of the endothelial permeability barrier. Recently, it was shown that endothelial cell stiffness per se plays a role in adhesion and transmigration of immune cells (84,85). Our previous studies also demonstrate that an increase in endothelial cell stiffness and force generation enhances endothelial angiogenic potential in 3D cultures in vitro (10,11) and in matrigels inserted in vivo (56).…”

Leukocyte transendothelial migration: A local affair

“…24 To find these spots of low resistance, lymphocytes dynamically probe the underlying endothelium by extending invadosome-like protrusions into its surface that deform the plasma membrane, depolymerize F-actin filaments at the membrane cortex and ultimately breach the barrier. 24,25 The authors suggest that leukocyte transmigration is guided by a common principle namely 'the path of least resistance'. 24 However, determining where the path of least resistance is present in vivo is very difficult, if not impossible.…”

“…24,25 The authors suggest that leukocyte transmigration is guided by a common principle namely 'the path of least resistance'. 24 However, determining where the path of least resistance is present in vivo is very difficult, if not impossible. The observations of tenertaxis for TEM are so far only performed in in vitro studies.…”

“…According to tenertaxis, leukocytes would prefer a site of low endothelial cytoskeletal density, while according to durotaxis leukocytes need an optimum cytoskeletal stiffness to cross the vessel wall. 24 This opposing arguments for determining the transendothelial migration 'hotspot' indicate that the mechanism that determines the TEM hotspot is likely an interdependent combination of the TEM factors chemo-, hapto-, duroand tenertaxis, where, dependent on specific (patho) physiological conditions, one factor may play a more dominant role over the other in determining the site for leukocytes to cross.…”

Cell-stiffness-induced mechanosignaling – a key driver of leukocyte transendothelial migration

“…Leukocytes probe the surface of the substrate (i.e. ECs) and sense local EC stiffness through ventral filopodia or invadosome-like protrusions Martinelli et al, 2014;Schaefer et al, 2014;Shulman et al, 2009). The mechanosensitive response of leukocytes to substrate stiffness is mediated by their integrins, which are force-generating mechanoreceptors (Roca-Cusachs et al, 2012;Ross et al, 2013).…”