TGFβ1 exacerbates blood-brain barrier permeability in a mouse model of hepatic encephalopathy via upregulation of MMP9 and downregulation of claudin-5

Recent studies have found that vasogenic brain edema is present during hepatic encephalopathy following acute liver failure and is dependent on increased matrix metalloproteinase 9 (MMP9) activity and downregulation of tight junction proteins. Furthermore, circulating transforming growth factor beta 1 (TGF beta 1) is increased following liver damage and may promote endothelial cell permeability. This study aimed to assess whether increased circulating TGF beta 1 drives changes in tight junction protein expression and MMP9 activity following acute liver failure. Blood-brain barrier permeability was assessed in azoxymethane (AOM)-treated mice at 6, 12, and 18 h post-injection via Evan's blue extravasation. Monolayers of immortalized mouse brain endothelial cells (bEnd.3) were treated with recombinant TGF beta 1 (rTGF beta 1) and permeability to fluorescein isothiocyanate-dextran (FITC-dextran), MMP9 and claudin-5 expression was assessed. Antagonism of TGF beta 1 signaling was performed in vivo to determine its role in blood-brain barrier permeability. Blood-brain barrier permeability was increased in mice at 18 h following AOM injection. Treatment of bEnd.3 cells with rTGF beta 1 led to a dose-dependent increase of MMP9 expression as well as a suppression of claudin-5 expression. These effects of rTGF beta 1 on MMP9 and claudin-5 expression could be reversed following treatment with a SMAD3 inhibitor. AOM-treated mice injected with neutralizing antibodies against TGF beta demonstrated significantly reduced blood-brain barrier permeability. Blood-brain barrier permeability is induced in AOM mice via a mechanism involving the TGF beta 1-driven SMAD3-dependent upregulation of MMP9 expression and decrease of claudin-5 expression. Therefore, treatment modalities aimed at reducing TGF beta 1 levels or SMAD3 activity may be beneficial in promoting blood-brain barrier integrity following liver failure.