Abstract
To shed light on the specific role of the transmembrane protein PECAM-1 in monocyte diapedesis, PECAM-1-GFP fusion vector was constructed and transfected into human umbilical vein endothelial cells (HUVECs). Since GFP was fused to the C-terminus (intracellular side) of PECAM-1, interactions of the PECAM-1 extracellular domain with monocytes can be kept intact. Three-dimensional-live-cell molecular imaging revealed that endothelial PECAM-1 was dynamically recruited to surround the transmigrating monocyte locally during paracellular diapedesis. This recruitment was not observed during transcellular diapedesis, which was only 5% of total diapedesis events. Three-dimensional image analysis showed a <1.5–1.8 fold increase of local PECAM-1 fluorescent signals near transmigrating monocytes within 20 min of paracellular events. Flow cytometric analysis also indicated a <1.4-fold increase of overall PECAM-1 signals from endothelial cells in 50 min of monocyte coincubation. The recruitment was not seen in the local region which was not associated with diapedesis events, which excludes the involvement of soluble factors secreted by monocytes. Blocking of neither monocyte adhesion nor transmigration induced the recruitment. These data indicate that local transmigration events, but not adhesion, or monocyte soluble factors, could induce the dynamic recruitment of endothelial PECAM-1 to transmigrating monocytes during paracellular diapedesis. [J Physiol Sci. 2008;58 Suppl:S61]
