The role of Connexin 43 gap junction formation in monocytes trans-endothelial migration.

Atherosclerosis is a chronic inflammatory disease characterised by the accumulation of monocytic cells and lipids within the sub-endothelial space by direct monocyte to endothelial cell contact through gap junctions (GJs). Both cell types express connexin 43 (Cx43) isoforms that permit the formation of GJs. This is enhanced by adhesion molecules in the presence of pro-inflammatory stimuli, such as tumour necrosis factor α (TNF-α). TNF-α is suggested to have a role in Cx43 expression mainly mediated through MAPK pathways over other intercellular pathways; however, to date the mechanism remains unclear. Experiments were carried out in the absence and presence of 25ng/ml TNF-α and the functional integrity of human umbilical vein endothelial cell (HUVEC) monolayers was assessed by measuring the trans-endothelial electrical resistance (TEER). The trans-endothelial migration (TEM) assay used as a model for the transmigration of monocytes to the sub-endothelial space. Monocytes were added to HUVEC monolayers, and cells which passed from one chamber to another were collected, marked with CD14+ and measured by flow cytometry. The efficiency of TEER and TEM was measured in: 1) the presence of the GJ inhibitor, 43GAP27; 2) HUVECs transfected with Cx43-siRNA; and 3) MAPK inhibitors, chelerythrine chloride (CHE). TEER measurements showed a reduction in the presence of TNF-α compared to the control cells (13.58±2.82Ω.cm2, 43.94±3.32Ω.cm2; n=6); however, when the protein kinase C (PKC) inhibitor CHE was added, the resistance was the same as in the control cells (48.64±3.62Ω.cm2, 45.76±4.83Ω.cm2; n=6). TNF-α enhanced the migration of monocytes (66.3±2.1%; n=3) compared to the control cells (9.9±4.5%; n=3; P<0.001), but this was prevented in monolayer also treated with CHE (13.70±2.45%; n=3; P