αB-crystallin/HspB5 regulates endothelial-leukocyte interactions by enhancing NF-κB-induced up-regulation of adhesion molecules ICAM-1, VCAM-1 and E-selectin

alpha B-crystallin is a small heat shock protein, which has pro-angiogenic properties by increasing survival of endothelial cells and secretion of vascular endothelial growth factor A. Here we demonstrate an additional role of alpha B-crystallin in regulating vascular function, through enhancing tumor necrosis factor alpha (TNF-alpha) induced expression of endothelial adhesion molecules involved in leukocyte recruitment. Ectopic expression of alpha B-crystallin in endothelial cells increases the level of E-selectin expression in response to TNF-alpha, and enhances leukocyte-endothelial interaction in vitro. Conversely, TNF-alpha-induced expression of intercellular adhesion molecule 1, vascular cell adhesion molecule 1 and E-selectin is markedly inhibited in endothelial cells isolated from alpha B-crystallin-deficient mice. This is associated with elevated levels of I kappa B in alpha B-crystallin deficient cells and incomplete degradation upon TNF-alpha stimulation. Consistent with this, endothelial adhesion molecule expression is reduced in inflamed vessels of alpha B-crystallin deficient mice, and leukocyte rolling velocity is increased. Our data identify alpha B-crystallin as a new regulator of leukocyte recruitment, by enhancing pro-inflammatory nuclear factor kappa B-signaling and endothelial adhesion molecule expression during endothelial activation.