Abstract 2951: Role Of Transcellular Transport During Fibrinogen-induced Increase In Pial Venular Permeability In Mice

Abstract

Many inflammatory diseases such as stroke, hypertension, and diabetes are accompanied by increased blood content of fibrinogen (Fg). We showed that high content of undegraded Fg causes macromolecular leakage in pial vessels and increases endothelial cell (EC) layer permeability affecting paracellular pathway causing changes in tight junction proteins. In this study we tested the hypothesis that Fg-induced cerebrovascular permeability involves transcellular pathway through activation of matrix metalloproteinase-9 (MMP-9). Fg (total blood content 4 mg/ml) or phosphate buffered saline (PBS) were infused to wild-type (WT, C57BL/6J) and MMP-9 gene knockout (MMP9-−) mice. After measuring pial venular leakage brain cortical cryo-sections were probed with antibodies against caveolin-1 (Cav-1) and plasmalemma vesicle associated protein-1 (PV-1) to define the role of functional caveolae in vascular permeability. Possible formation of caveolae also was observed in mouse brain endothelial cells (MBECs) with total internal reflection fluorescence microscopy. Expression of Cav-1 and PV-1 was more in Fg-infused (155 ± 4 % and 85 ± 4 % of baseline, respectively) compared to PBS-infused (110 ± 3 % and 51 ± 6 % of baseline, respectively) WT animals. In MMP9-− mice, Fg induced greater expression of Cav-1 and PV-1 (72 ± 4 % and 46 ± 3 % of baseline, respectively) than PBS infusion (43 ± 2 % and 18 ± 3 % of baseline, respectively), but the effects were lesser than in WT mice. High content of Fg increased formation of functional caveolae in MBECs compared to that in cells treated with PBS. These data suggest that at an increased level Fg compromises cerebrovascular integrity by enhancing caveolae formation. Thus, at higher contents, Fg increases microvascular permeability altering the transcellular transport in addition to the paracellular transport.