Three-dimensional forces exerted by leukocytes and vascular endothelial cells dynamically facilitate diapedesis

Abstract

Leukocyte transmigration across vessel walls is a critical step in the innate immune response. Upon their activation and firm adhesion to vascular endothelial cells (VECs), leukocytes preferentially extravasate across junctional gaps in the endothelial monolayer (paracellular diapedesis). It has been hypothesized that VECs facilitate paracellular diapedesis by opening their cell-cell junctions in response to the presence of an adhering leukocyte. However, it is unclear how leukocytes interact mechanically with VECs to open the VEC junctions and migrate across the endothelium. In this study, we measured the spatial and temporal evolution of the 3D traction stresses generated by the leukocytes and VECs to elucidate the sequence of mechanical events involved in paracellular diapedesis. Our measurements suggest that the contractile stresses exerted by the leukocytes and the VECs can separately perturb the junctional tensions of VECs to result in the opening of gaps before the initiation of leukocyte transmigration. Decoupling the stresses exerted by the transmigrating leukocytes and the VECs reveals that the leukocytes actively contract the VECs to open a junctional gap and then push themselves across the gap by generating strong stresses that push into the matrix. In addition, we found that diapedesis is facilitated when the tension fluctuations in the VEC monolayer were increased by proinflammatory thrombin treatment. Our findings demonstrate that diapedesis can be mechanically regulated by the transmigrating leukocytes and by proinflammatory signals that increase VEC contractility.

Balance of mechanical forces drives endothelial gap formation and may facilitate cancer and immune-cell extravasation

“…Our model predictions of gap opening frequency and lifetime at both cell vertices and borders are validated by experiments observing such gaps in endothelial monolayers in the absence of any extravasating cell. 4 The results thus challenge the paradigm that all extravasating cells primarily cause gap opening through interactions with the endothelium [1,8,31]. We then show experimentally that extravasating cancer cells indeed primarily extravasate at vertices, in line with similar observations for neutrophils [32].…”

Lymphocyte mechanotransduction: The regulatory role of cytoskeletal dynamics in signaling cascades and effector functions

“…By utilizing 3D TFM, it was shown that leukocytes exert force to open junctions between vascular endothelial cells. Under inflammatory conditions, less traction stress is required for diapedesis, facilitating leukocyte extravasation . Because less traction force is required for transendothelial migration during inflammation, this mechanism may also protect nuclear and DNA integrity, both of which were shown to undergo mechanical damage during invasive migration …”

“…Under inflammatory conditions, less traction stress is required for diapedesis, facilitating leukocyte extravasation. 9 Because less traction force is required for transendothelial migration during inflammation, this mechanism may also protect nuclear and DNA integrity, both of which were shown to undergo mechanical damage during invasive migration. 65 Accordingly, another recent study demonstrated that T cells can sense 3D environments and density of the collagen matrix.…”

“…Studying processes of mechanotransduction/mechanosensation in nonadherent cells such as leukocytes and erythrocytes is more complex, given that they are subject to very different types of physical stress compared to adherent cells in solid tissues. Different forces are applied to and sensed by immune cells during circulation through blood and lymphatic vessels, and when they traverse into tissues . Furthermore, force is applied to and sensed by lymphocytes during cell/cell contacts .…”

“…Different forces are applied to and sensed by immune cells during circulation through blood and lymphatic vessels, and when they traverse into tissues. [6][7][8][9] Furthermore, force is applied to and sensed by lymphocytes during cell/cell contacts. 10 Advanced technologies such as atomic force microscopy (AFM), traction force microscopy (TFM), 11 tension gauge tethers, 12 and molecular force sensors 13 are enabling researchers to directly measure forces that these cells apply to different solid substrates.…”