Fibrinogen Protects Against Barrier Dysfunction Through Maintaining Cell Surface Syndecan-1 In Vitro.

We have shown that fresh frozen plasma's (FFP) protection of pulmonary endothelial barrier integrity following hemorrhagic shock is due in part to restoration of endothelial syndecan-1. In the present study, we investigated the role of fibrinogen, a major component of FFP, as an endothelial protector and hypothesize that fibrinogen stabilizes cell surface syndecan-1 to restore endothelial barrier integrity. Pulmonary endothelial cells were incubated in FFP, fibrinogen, or lactated Ringers (LR) then immunostained with anti-syndecan-1 or fibrinogen and barrier integrity assessed. In some experiments, cells were exposed to fibrinogen depleted plasma. Cell surface syndecan-1 was increased by FFP and fibrinogen compared with LR-treated cells while barrier integrity was augmented by FFP and fibrinogen compared with LR. The physiological concentration of 2.5 mg/mL fibrinogen was sufficient to increase cell surface syndecan-1. Colocalization and co-immunoprecipitation experiments demonstrated that fibrinogen associates with syndecan-1. Fibrinogen-deficient plasma was unable to augment sydnecan-1 immunostaining and lost its endothelial protective effect on barrier integrity. These data suggest that in vitro, fibrinogen associated with cell surface syndecan-1 and enhanced endothelial barrier integrity.