Fibrinogen alters mouse brain endothelial cell layer integrity affecting vascular endothelial cadherin

Many inflammatory diseases are associated with elevated blood concentration of fibrinogen (Fg) leading to vascular dysfunction. We showed that pathologically high (4 mg/ml) content of Fg disrupts integrity of endothelial cell (EC) layer and causes macromolecular leakage affecting tight junction proteins. However, role of adherence junction proteins, particularly vascular endothelial cadherin (VE-cadherin) and matrix metalloproteinase-9 (MMP-9) in this process is not clear. We tested the hypothesis that at high levels Fg affects integrity of mouse brain endothelial cell (MBEC) monolayer through activation of MMP-9 and downregulation of VE-cadherin expression and in part its translocation to the cytosol. The effect of Fg on cultured MBEC layer integrity was assessed by measuring transendothelial electrical resistance. Cellular expression and translocation of VE-cadherin were assessed by Western blot and immunohistochemical analyses, (respectively). Our results suggest that high content of Fg decreased VE-cadherin expression at protein and mRNA levels. Fg induced translocation of VE-cadherin to cytosol, which led to disruption of cell-to-cell interaction and cell to subendothelial matrix attachment. Fg-induced alterations in cell layer integrity and their attachment were diminished during inhibition of MMP-9 activity. Thus Fg compromises EC layer integrity causing downregulation and translocation of VE-cadherin and through MMP-9 activation. These results suggest that increased level of Fg could play a significant role in vascular dysfunction and remodeling.