Abstract
We investigated the role of NF-kappaB activation by the bacterial product lipopolysaccharide (LPS) in inducing caveolin-1 (Cav-1) expression and its consequence in contributing to the leakiness of the endothelial barrier. We observed that LPS challenge of human lung microvascular endothelial cells induced concentration- and time-dependent increases in expression of Cav-1 mRNA and protein. The NEMO (NF-kappaB essential modifier binding domain)-binding domain peptide (IkB kinase (IKK)-NEMO-binding domain (NBD) peptide), which prevents NF-kappaB activation by inhibiting the interaction of IKKgamma with the IKK complex, blocked LPS-induced Cav-1 mRNA and protein expression. Knockdown of NF-kappaB subunit p65/RelA expression with small interfering RNA also prevented LPS-induced Cav-1 expression. Caveolae open to the apical and basal plasmalemma of endothelial cells increased 2-4-fold within 4 h of LPS exposure. IKK-NBD peptide markedly reduced the LPS-induced increase in the number of caveolae as well as transendothelial albumin permeability. These observations were recapitulated in mouse studies in which IKK-NBD peptide prevented Cav-1 expression and interfered with the increase in lung microvessel permeability induced by LPS. Thus, LPS mediates NF-kappaB-dependent Cav-1 expression that results in increased caveolae number and thereby contributes to the mechanism of increased transendothelial albumin permeability.