Parallel 8: Novel Approaches in Diagnosis and Treatment in NAFLD and NASH
Authors: Cynthia Leveille-Webster, Andrea Johnston, Mohammed Anwer, Kunimaro Furuta, Yuichi Yoshida, Takashi Kizu, Satoshi Ogura, Mayumi Egawa, Norihiro Chatani, Yoshihiro Kamada, Shinichi Kiso, Tetsuo Takehara, Tetsuo Takehara -Grant, Won Kim, June Lee, Chun Lee, Jong Yeon, Byeong Kim, Yoon Kim, Smitha Marri, Mazen Noureddin, Thomas Schiano, Mohammad Siddiqui, Rohit Loomba, Claude Sirlin, Brandon Ang, Ricki Betten- Court, Rashmi Jain, Joanie Salotti, Linda Soaft, Jonathan Hooker, Yuko Kono, Archana Bhatt, Laura Hernandez, Phirum Nguyen, William Haufe, Catherine Hooker, Meng Yin, Richard Ehman, Grace Lin, Mark Valasek, David Brenner, Lisa Richards
Journal: Hepatology (2014)

Background & Aims: Acute liver failure (ALF) is characterized by severe hepatocyte death and impaired liver regeneration.Acetaminophen (APAP) overdose is a leading cause of ALF in Western countries.In APAP hepatotoxicity, it has been shown that mitochondrial dysfunction is critical and that mitochondrial translocation of a stress MAP kinase, JNK is associated with this process.We previously demonstrated that Grb2-associated binder 1 (Gab1) adaptor protein transmits mitogenic signals via a MAP kinase, ERK in vitro and in vivo.However, the role of Gab1 in hepatocyte death during APAP-induced ALF has remained unclear.Here, we investigated the role of Gab1 in this process.Method: Hepatocyte specific Gab1 knock-out (KO) and wild-type (WT) mice were intraperitoneally injected with APAP (250 mg/kg bw) to induce ALF.Results: KO mice showed significantly higher mortality rate compared with WT mice at 72 hours after APAP treatment (75% in KO n=12 vs. 25% in WT n=12, p<0.05).This increased mortality in KO mice was associated with elevated serum ALT levels (p<0.05),increased TUNEL positive hepatocytes (p<0.05), and severe centrilobular liver necrosis (p<0.01) at 6 hours after APAP treatment.KO mice also showed a 2.4-fold increase in serum levels of high mobility group box 1 (HMGB-1) (p<0.01), a danger signaling molecule, indicating higher degree of hepatocyte necrosis in KO mice.To clarify the mechanisms of enhanced hepatocyte necrosis in KO mice, we next examined whether loss of Gab1 affected the mitochondrial function during APAP-induced ALF.At 1.5 hours after APAP treatment, KO mice showed enhanced mitochondrial translocation of JNK compared with WT mice, accompanied by increased release of mitochondrial enzymes such as Apoptosis-inducing factor and Endonuclease G into the cytosol.These data suggested that loss of Gab1 might cause hepatocyte necrosis through mitochondrial dysfunction and subsequent nuclear DNA fragmentation.Finally, we examined compensatory proliferation in hepatocytes surrounding necrotic areas after APAP treatment.Ki67 stating demonstrated that KO mice had a 2-fold decrease (p<0.05) in the number of proliferating hepatocytes.Consistent with data of Ki67 staining, the mitogenic signals, such as ERK and AKT were markedly reduced in KO mice, suggesting that Gab1 might regulate both hepatocyte death and compensatory proliferation during APAP-induced ALF.Conclusion: In a mouse model of ALF, loss of Gab1 in hepatocytes resulted in higher mortality with enhanced mitochondrial dysfunction and hepatocyte necrosis.Our data further suggested that Gab1 could be a novel therapeutic target for the treatment of ALF