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Abundant evidence documents the highly proinflammatory actions of lysophosphatidylcholine (LPC). Further, LPC, found in high amounts in oxidized low-density lipoprotein (LDL), is implicated as an atherogenic factor. In endothelial cells, LPC impairs endothelial barrier function through GPR4, a novel receptor hypothesized to be sensitive to LPC and protons. The authors investigated the stimulation by LPC or low pH of GPR4 in human brain microvascular endothelial cells (HBMECs) and whether the activated GPR4 regulates in vitro monocyte transmigration. The results indicated that HBMECs stimulated by LPC (5 μM), but not low pH, showed a twofold increase in monocyte transmigration. Using retroviruses containing siRNA to GPR4, a > 60% reduction of GPR4 expression resulted in blockade of the LPC-stimulated transmigration. The inhibited response was restored by co-expression with an small interference RNA (siRNA)-resistant, but functional, GPR4 mutant construct. To investigate potential signaling mechanisms, the siRNA-mediated knockdown of GPR4 also prevented LPC-induced RhoA activation. C3 transferase, a Rho inhibitor, prevented ∼ ∼ 65% of the LPC-stimulated transmigration. LPC also increased MLC phosphorylation by 5 min, which was inhibited by the Rho kinase inhibitor, Y-27632 (10 μM) or ML-7 (myosin light chain kinase (MLCK) inhibitor). The findings indicate that the proinflammatory and atherogenic LPC stimulated endothelial GPR4, which promoted monocyte transmigration through a RhoA-dependent pathway. [ABSTRACT FROM AUTHOR]

Discusses the hypothesis that serine/threonine protein phosphatases may regulate protein kinase C, a critical signaling molecule in barrier dysfunction in the promotion of barrier recovery. Expression of protein phosphatases 1, 2A and 2B; Effects of inhibitors on thrombin-induced protein kinase C activity and phosphorylation.

Studies the role of Ca2+ in mediating the hydrogen peroxide-induced increase in endothelial permeability to 125I-labeled albumin using bovine pulmonary microvessel endothelial cells. Culture of pulmonary microvessel endothelial cell monolayers; Intracellular Ca2+ transient; H2O2 challenge protocol.

Focuses on the regulation of vascular endothelial barrier function. Modulation of actin-based systems; Maintenance of endothelial integrity; Role of cadherins in regulating the formation of tight junctions; Association of increased phosphorylation with actin reorganization.

Investigates the involvement of the 14-residue thrombin receptor activation peptide SFLLRNPNDKYEPF in mediating the pulmonary vasoconstriction in response to alpha-thrombin. Lung perfusion preparation; Smooth muscle cell culture; Intracellular calcium measurements; Peptide synthesis.

Investigates the effect of site-specific thrombin receptor antibodies on calcium signaling and endothelial permeability. Effect of thrombin on albumin permeability and intracellular calcium concentration (Ca2+)i in human microvascular endothelial cells; Influence of the thrombin receptor Abs on thrombin-induced increase in (Ca2+)i.

Editorial. Comments on the role of lysophospholipids in the regulation of endothelial barrier function. Identification of lysophospholipid ligands; Activation of platelet-activating factor; Promotion of endothelial barrier restrictiveness.