An Increase in Endothelial Intracellular Calcium and F-Actin Precedes the Extravasation of Interleukin-2-Activated Lymphocytes

Actin filament reorganization is a key step in lung inflammation induced by systemic inflammatory response syndrome

Acute lung injury (ALI) induced by systemic inflammatory response syndrome (SIRS) is characterized by deterioration in pulmonary function and leukocyte-associated lung inflammation. Actin fragment (F-actin) reorganization is required for leukocyte activation, adhesion, and transcription of inflammatory factors. We tested the hypothesis that F-actin plays a central role in SIRS-induced ALI. ALI was produced in a rat model with extracorporeal circulation. Cytochalasin B (CB) pretreatment to block F-actin reorganization improved oxygenation and reduced BAL inflammatory factors and pulmonary neutrophil sequestration, but did not reduce the adhesive molecules of blood leukocytes. We challenged blood neutrophils with TNF-α in vitro to explore the underlying mechanisms. Upon activation, neutrophils became polarized and formed a protrusive leading edge, with an aggregation of CD11b molecules. This effect could be blocked by CB, leading to reduced neutrophil adhesion. In addition, after LPS challenge, we observed F-actin reorganization and the up-regulation of inflammatory factors in pulmonary monocytes, which could also be blocked by CB pretreatment. F-actin reorganization initiates lung inflammation via increased blood neutrophil adhesion and migration, and by the production of inflammatory factors by pulmonary monocytes. Thus, blocking F-actin reorganization may potentially prevent and treat SIRS-induced ALI.

An in vitro model to study the role of endothelial rho GTPases during leukocyte transendothelial migration

Tissue injury induces release of cytokines that stimulate the expression of adhesion receptors in the endothelial wall of neighboring vessels. These endothelial receptors recruit leukocytes from the bloodstream and facilitate their transendothelial migration (TEM) toward the inflamed area. The molecules involved in leukocyte-endothelium interaction and TEM have been studied in vivo and in vitro over the past 20 years. Human umbilical vein endothelial cells (HUVECs) are a popular in vitro model to analyze TEM, and have been used to investigate the role of Rho GTPases in this process. Here we describe methods to activate HUVECs, to investigate Rho GTPase-activation by the endothelial adhesion receptor ICAM-1, and to inhibit or activate Rho GTPases using C3 transferase or adenoviruses coding for dominant negative or constitutive active Rho GTPases. Finally, we describe how to image and quantitate leukocyte TEM by digital time-lapse microscopy.

Rho GTPases and leucocyte-induced endothelial remodelling

Leucocytes in the bloodstream respond rapidly to inflammatory signals by crossing the blood vessel wall and entering the tissues. This process involves adhesion to, and subsequent transmigration across, the endothelium, mediated by a cascade of interactions between adhesion molecules and stimulation of intracellular signalling pathways in both leucocytes and endothelial cells. This leads to changes in endothelial cell morphology that assist leucocyte extravasation, including endothelial cell contraction, intercellular junction disruption, increased permeability, remodelling of the endothelial apical surface and alterations in vesicle trafficking. Rho GTPases play a central role in many of the endothelial responses to leucocyte interaction. In this review, we discuss recent findings on leucocyte-induced alterations to endothelial cells, and the roles of Rho GTPases in these responses.

In vitro assessment of human endothelial cell permeability: effects of inflammatory cytokines and dengue virus infection

Electrical resistance across human umbilical vein endothelial cells (HUVECs) was measured using an electrical cell sensor system. The transendothelial electrical resistance (TEER) value was used to estimate the permeability through endothelial cells in vitro. Decrease in the TEER value was associated with increase in the passage of albumin through endothelial cells in the albumin permeability assay. The effects of cytokines and dengue virus infection on the permeability of HUVECs were examined by measuring the TEER value. Tumor necrosis factor alpha (TNF-alpha) at 1 and 0.1 microg/ml decreased the TEER value, but TNF-alpha at lower dose did not. Interferon-gamma (IFN-gamma) at 1 microg/ml also decreased the TEER value. In contrast, interleukin-2 (IL-2), interleukin-6 (IL-6), interleukin-8 (IL-8), interleukin-10 (IL-10) or interferon-beta (IFN-beta) did not decrease the TEER value. The decrease in the TEER value was associated with the morphological changes of HUVECs. Dengue virus infection at a multiplicities of infection (m.o.i.) of 5 pfu/cell decreased the TEER value. Infection at an m.o.i. of 0.5 pfu/cell did not decrease the TEER value; however, addition of 0.01 microg/ml of TNF-alpha to these infected endothelial cells decreased the TEER value. The results suggest that TNF-alpha and dengue virus infection decrease synergistically the TEER value of endothelial cells. The TEER method is easy, reliable and can be applicable to further analysis of the increase in the permeability of endothelial cells in vitro induced by inflammatory cytokines and dengue virus infection.

Proinflammatory effects of copper deficiency on neutrophils and lung endothelial cells

Dietary copper deficiency increases the accumulation of circulating neutrophils in the rat lung microcirculation. This process includes neutrophil adhesion to, migration along, and emigration though the vascular endothelium. The current study was designed to examine the role of copper in each of these steps. Neutrophils were isolated from rats fed either a copper-adequate (CuA, 6.1 microg Cu/g diet) or copper-deficient diet (CuD, 0.3 microg Cu/g diet) for 4 weeks. First, transient and firm adhesion of neutrophils to P-selectin in a flow chamber showed there were more adhered CuD neutrophils than CuA ones. This effect is probably caused by the increased expression of CD11b that was observed in the current study. Second, the evaluation of neutrophil migration under agarose showed that the CuD neutrophils moved farther than the CuA group in response to IL-8 but not fMLP; this suggests an increased sensitivity to a CD11/CD18-independent signalling pathway. Third, the contractile mechanism of endothelial cells was studied. Elevated F-actin formation in Cu-chelated lung microvascular endothelial cells suggests that neutrophil emigration may be promoted by enhanced cytoskeletal reorganization of the endothelium during copper deficiency. Combined, these results support the theory that dietary copper deficiency has proinflammatory effects on both neutrophils and the microvascular endothelium that promote neutrophil-endothelial interactions.

Oxidant stress and endothelial cell dysfunction

Reactive oxygen species (ROS) are generated at sites of inflammation and injury, and at low levels, ROS can function as signaling molecules participating as signaling intermediates in regulation of fundamental cell activities such as cell growth and cell adaptation responses, whereas at higher concentrations, ROS can cause cellular injury and death. The vascular endothelium, which regulates the passage of macromolecules and circulating cells from blood to tissues, is a major target of oxidant stress, playing a critical role in the pathophysiology of several vascular diseases and disorders. Specifically, oxidant stress increases vascular endothelial permeability and promotes leukocyte adhesion, which are coupled with alterations in endothelial signal transduction and redox-regulated transcription factors such as activator protein-1 and nuclear factor-kappaB. This review discusses recent findings on the cellular and molecular mechanisms by which ROS signal events leading to impairment of endothelial barrier function and promotion of leukocyte adhesion. Particular emphasis is placed on the regulation of cell-cell and cell-surface adhesion molecules, the actin cytoskeleton, key protein kinases, and signal transduction events.