Differing mechanisms of leukocyte recruitment and sensitivity to conditioning by shear stress for endothelial cells treated with tumour necrosis factor‐α or interleukin‐1β

Abstract

1 The cytokines tumour necrosis factor-a (TNFa) and interleukin-1b (IL-1B) induce endothelial cells to recruit leukocytes. However, the exact adhesion and activation mechanisms induced by each cytokine, and their relative sensitivities to modulation by endothelial exposure to shear stress remain unclear.2 We cultured human umbilical vein endothelial cells (HUVEC) in glass capillaries at various shear stresses, with TNFa or IL-1B added for the last 4 h. Subsequently, human neutrophils were perfused over the HUVEC, and adhesion and migration were recorded. 3 Both cytokines induced dose-dependent capture of neutrophils. However, while conditioning of HUVEC by increasing shear stress for 24 h diminished their response to TNFa, the response of HUVEC to IL-1B was similar at all shear stresses. The differing sensitivities were evident at levels of adhesive function and mRNA for adhesion molecules and chemokines. 4 Analysis of nuclear factor kB (NF-kB)/Rel family of transcription factors showed that their expression and activation were modified by exposure to shear stress, but did not obviously explain differential responses to TNFa and IL-1B. 5 Antibodies against selectins were effective against capture of neutrophils on TNFa-treated but not IL-1B-treated HUVEC. Stable adhesion was supported by b2-integrins in each case. Activation of neutrophils occurred dominantly through CXC-chemokine receptor 2 (CXCR2) for TNFa-treated HUVEC, while blockade of CXCR1, CXCR2 and of platelet-activating factor receptors caused additive inhibition of migration on IL-1B-treated HUVEC. 6 The mechanisms which underlie neutrophil recruitment, and their modulation by the haemodynamic environment, differ between cytokines. Interventions aimed against leukocyte recruitment may not operate equally in different inflammatory milieu.

Chemokine- and adhesion-dependent survival of neutrophils after transmigration through cytokine-stimulated endothelium

“…Antibodies against CXC chemokine receptor 1 (CXCR1) or CXCR2 (Clones 501 and 19, Biosource International Inc., Camarillo, CA) were used at 2 μg/ml, according to the manufacturer's recommendation. In recent, flow-based studies, we have found these antibodies to inhibit neutrophil migration through TNF-treated HUVEC and also to increase the percentage of the captured cells undergoing rolling [25,26]. This indicates that they inhibit migration through blockade of activation rather than by mimicking the natural CXC chemokine agonists.…”

Endothelial-Dependent Mechanisms of Leukocyte Recruitment to the Vascular Wall

“…In response to TNF-␣, neutrophil recruitment (adherence and transmigration) was reduced in a shear-dependent manner, with a concomitant reduction in cytokine-induced expression of E-selectin, IL-8, and Gro-␣, whereas no such difference was observed for IL-1␤. 62 The mechanism underlying these observations remains unidentified, but the emergence of flowinduced transcription factors such as Kruppel-like factor 2 (KLF)2 might provide an explanation (see below for detailed discussion on KLF2).…”

The Role of Platelet-Endothelial Cell Adhesion Molecule-1 in Atheroma Formation Varies Depending on the Site-Specific Hemodynamic Environment

“…20 However, cultured EC, which had been subjected to PECAM-1 small interfering RNA knock down, did not align in response to laminar high shear, but remained polygonal, 20 a phenotype found in areas of arteries prone to atherogenesis. Generally, laminar shear stress suppresses the inflammatory responses of EC, 21,22 and we have recently shown that this protective effect also requires expression of PECAM-1. 23 Thus, taken together, these results indicate that PECAM-1 may play roles in the proinflammatory response believed to promote atherogenesis in regions of disturbed flow and in the protective effects of laminar, high shear stress.…”