Endothelial cell (EC) barrier dysfunction results in increased vascular permeability, leading to increased mass transport across the vessel wall and leukocyte extravasation, the key mechanisms in pathogenesis of tissue
inflammation and
edema. We have previously demonstrated that
OxPAPC (oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine) significantly enhances vascular endothelial barrier properties in vitro and in vivo and attenuates endothelial hyperpermeability induced by inflammatory and edemagenic agents via Rac and Cdc42
GTPase dependent mechanisms. These findings suggested potential important therapeutic value of barrier-protective oxidized
phospholipids. In this study, we examined involvement of signaling complexes associated with
caveolin-enriched microdomains (
CEMs) in barrier-protective responses of human pulmonary ECs to
OxPAPC. Immunoblotting from
OxPAPC-treated ECs revealed
OxPAPC-mediated rapid recruitment (5 minutes) to
CEMs of the
sphingosine 1-phosphate receptor (S1P(1)), the
serine/threonine kinase Akt, and the Rac1
guanine nucleotide exchange factor Tiam1 and phosphorylation of
caveolin-1, indicative of signaling activation in
CEMs. Abolishing CEM formation (
methyl-beta-cyclodextrin) blocked
OxPAPC-mediated Rac1 activation, cytoskeletal reorganization, and EC barrier enhancement. Silencing (
small interfering RNA) Akt expression blocked
OxPAPC-mediated S1P(1) activation (
threonine phosphorylation), whereas silencing S1P(1) receptor expression blocked
OxPAPC-mediated Tiam1 recruitment to
CEMs, Rac1 activation, and EC barrier enhancement. To confirm our in vitro results in an in vivo murine model of
acute lung injury with pulmonary vascular hyperpermeability, we observed that selective lung silencing of
caveolin-1 or S1P(1) receptor expression blocked
OxPAPC-mediated protection from
ventilator-induced lung injury. Taken together, these results suggest Akt-dependent transactivation of S1P(1) within
CEMs is important for
OxPAPC-mediated cortical actin rearrangement and EC barrier protection.