Proinflammatory Activation Pattern of Human Umbilical Vein Endothelial Cells Induced by IL-1β, TNF-α, and LPS

Endothelial cells play a critical role in inflammation by responding to several endogenous and exogenous proinflammatory stimuli. The three most studied factors that provide inflammatory signals to endothelial cells are lipopolysaccharide (LPS), tumor necrosis factor (TNF)-α, and interleukin (IL)-1β; however, their effects on endothelial cells were thoroughly compared at the level of gene expression only. Therefore, our aim was to assess the differences in the signaling pathways, adhesion molecules, and cytokines induced by proinflammatory factors in human umbilical vein endothelial cells (HUVEC). In this study, we demonstrated that signaling of LPS was less effective than that of IL-1β, and was significantly slower than that ofTNF-α and IL-1β, which can be partially explained by the special localization of Toll-like receptor 4 (TLR4). We showed that TLR4 is mainly localized in Golgi apparatus in HUVEC. The proinflammatory capacity of TNF-α was similar to that of IL-1β in inducing NF-κB nuclear translocation, while IL-1β was the strongest activator of MAPK pathways. Moreover, expression of E-selectin, IL-6, and IL-8 was induced most efficiently by IL-1β, while LPS and TNF-α had less effect, whereas we did not find such a difference in ICAM-1 and MCP-1 expression. Due to the higher induction of E-selectin and IL-8, IL-1β might have more important role in neutrophil recruitment than LPS and TNF-α. By above-mentioned parameters we identified a signaling and expression pattern for the three proinflammatory molecules. This pattern illustrates how complex a proinflammatory process can be, and may enable us to predict and compare the pathomechanism of various inflammatory diseases.