Occludin Is Regulated by Epidermal Growth Factor Receptor Activation in Brain Endothelial Cells and Brains of Mice with Acute Liver Failure

Mechanisms of brain edema in acute liver failure (ALF) are not completely understood. We recently demonstrated that matrix metalloproteinase 9 (MMP-9) induces significant alterations to occludin in brain endothelial cells in vitro and in brains of mice with experimental ALF (Hepatology 2009; 50: 1914). In this study we show that MMP-9-induced transactivation of epidermal growth factor receptor (EGFR) and p38 MAPK/NF kappa B (mitogen-activated protein kinase/nuclear factor-kappa B) signals participate in regulating brain endothelial occludin level. Mouse brain endothelial bEnd3 cells were exposed to MMP-9 or p38 MAPK up-regulation in the presence and absence of EGFR inhibitor, p38 MAPK inhibitor, NF kappa B inhibitor, and/or appropriate small interfering RNA. Reverse-transcription polymerase chain reaction (RT-PCR) and western blotting were used for messenger RNA and protein expression analyses. Immunohistochemical staining and confocal microscopy were used to demonstrate cellular EGFR activation. Intraperitoneal azoxymethane was use to induce ALF in mice. Brains of comatose ALF mice were processed for histological and biochemical analyses. When bEnd3 cells were exposed to MMP-9, EGFR was significantly transactivated, followed by p38 MAPK activation, I-kappa B alpha (I kappa B alpha) degradation, NF kappa B activation, and suppression of occludin synthesis and expression. Similar EGFR activation and p38 MAPK/NF kappa B activation were found in the brains of ALF mice, and these changes were attenuated with GM6001 treatment. Conclusion: EGFR activation with p38 MAPK/NF kappa B signaling contributes to the regulation of tight junction integrity in ALF. EGFR activation may thus play an important role in vasogenic brain edema in ALF. (HEPATOLOGY 2011;53:1294-1305)