Abstract 4742: Egfl7 Suppresses Endothelial ICAM-1 Expression in Response to H/R Injury
Background Egfl7 is a chemoattractant for endothelial cells and its expression is restricted to endothelial cells. Hypoxia/reperfusion (H/R) induced endothelial injury that occurs during transplantation contributes to the subsequent development of allograft vasculopathy. We investigated the effect of Egfl7 on endothelial cell intercellular adhesion molecule-1 (ICAM-1) expression in response to H/R injury.
Methods HCAEC (n±4 per group) were submitted to 24h of hypoxia (PO2 <0.1%) followed by 12h of normoxia (PO2=21%) in the presence or absence of Egfl7 (100 ng/mL). Normoxic controls were incubated for 36h at PO2=21%. Cell surface expression of ICAM-1 was assessed by flow cytometry. The presence of NFkB in nuclear and cytosolic protein fractions and IkB-α in the cytosolic fraction was assessed by Western blot analysis.
Results Incubation with Egfl7 during H/R prevented ICAM-1 upregulation (80±2.5% of control) compared to H/R alone (114±10% of control), p<0.05. NFkB nuclear localization upon H/R injury was blocked by Egfl7 administration (cytosolic/nuclear ratio of 0.93±0.02 vs 1.42±0.27, p<0.01). IkB-α protein level was significantly reduced upon H/R injury (25±5% of control expression, p<0.01), however, concurrent incubation with Egfl7 attenuated this reduction (49±6% of control expression, p<0.01 when compared to H/R injury alone).
Conclusions Our study reveals the novel observation that Egfl7 inhibits coronary artery endothelial cell expression of ICAM-1 subsequent to H/R injury. Mechanistically, Egfl7 prevented NFkB nuclear localization and augmented IkB-α protein levels, suggesting that it inhibits NFkB activation - a key step in the inflammatory activation of endothelial cells. Egfl7 may be protective against H/R injury incurred during transplantation and may modulate the events that lead to the development of graft vasculopathy.