Basic Study
Copyright ©The Author(s) 2016. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Jul 28, 2016; 22(28): 6509-6519
Published online Jul 28, 2016. doi: 10.3748/wjg.v22.i28.6509
c-Jun N-terminal kinase-mediated Rubicon expression enhances hepatocyte lipoapoptosis and promotes hepatocyte ballooning
Akiko Suzuki, Keisuke Kakisaka, Yuji Suzuki, Ting Wang, Yasuhiro Takikawa
Akiko Suzuki, Keisuke Kakisaka, Yuji Suzuki, Ting Wang, Yasuhiro Takikawa, Division of Hepatology, Department of Internal Medicine, Iwate Medical University, Morioka 0208505, Japan
Author contributions: Suzuki A performed in vivo and in vitro studies and wrote the paper; Kakisaka K designed the experiments. Suzuki Y and Wang T analyzed the data; Takikawa Y supervised the study and revised the paper; all authors drafted the article and made critical revisions related to the intellectual content of the manuscript, and approved the final version of the article to be published.
Supported by KAKENHI Grant, No. 16K21307.
Institutional animal care and use committee statement: All of the animal experiments were approved by the Animal Care and Use Committee of Iwate Medical University (Morioka, Japan; 25-025).
Conflict-of-interest statement: There is no conflict-of-interest.
Data sharing statement: No additional data are available.
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See:
Correspondence to: Keisuke Kakisaka, MD, PhD, Assistant Professor, Division of Hepatology, Department of Internal Medicine, Iwate Medical University, 19-1 Uchimaru, Iwate, Morioka 0208505, Japan.
Telephone: +81-19-6515111 Fax: +81-19-6526664
Received: April 5, 2016
Peer-review started: April 6, 2016
First decision: May 12, 2016
Revised: May 24, 2016
Accepted: June 13, 2016
Article in press: June 13, 2016
Published online: July 28, 2016

AIM: To clarify the relationship between autophagy and lipotoxicity-induced apoptosis, which is termed “lipoapoptosis,” in non-alcoholic steatohepatitis.

METHODS: Male C57BL/6J mice were fed a high-fat diet (HFD) for 12 wk, after which the liver histology and expression of proteins such as p62 or LC3 were evaluated. Alpha mouse liver 12 (AML12) cells treated with palmitate (PA) were used as an in vitro model.

RESULTS: LC3-II, p62, and Run domain Beclin-1 interacting and cysteine-rich containing (Rubicon) proteins increased in both the HFD mice and in AML12 cells in response to PA treatment. Rubicon expression was decreased upon c-Jun N-terminal kinase (JNK) inhibition at both the mRNA and the protein level in AML12 cells. Rubicon knockdown in AML12 cells with PA decreased the protein levels of both LC3-II and p62. Rubicon expression peaked at 4 h of PA treatment in AML12, and then decreased. Treatment with caspase-9 inhibitor ameliorated the decrease in Rubicon protein expression at 10 h of PA and resulted in enlarged AML12 cells under PA treatment. The enlargement of AML12 cells by PA with caspase-9 inhibition was canceled by Rubicon knockdown.

CONCLUSION: The JNK-Rubicon axis enhanced lipoapoptosis, and caspase-9 inhibition and Rubicon had effects that were cytologically similar to hepatocyte ballooning. As ballooned hepatocytes secrete fibrogenic signals and thus might promote fibrosis in the liver, the inhibition of hepatocyte ballooning might provide anti-fibrosis in the NASH liver.

Keywords: Ballooned hepatocyte, Caspase 9, c-Jun N-terminal kinase, Rubicon, SP600125

Core tip: Autophagy is interrupted in both in vivo and in vitro non-alcoholic steatohepatitis (NASH) models, and impaired autophagy is mediated by Run domain Beclin-1 interacting and cysteine-rich containing (Rubicon) protein expression via c-Jun N-terminal kinase phosphorylation. Rubicon expression appears prior to apoptosis and enhances palmitate toxicity in the hepatocytes, and caspase-9 decreases Rubicon at the protein level during lipoapoptosis. Caspase-9 inhibition with Rubicon expression induces both hepatocyte enlargement and endoplasmic reticulum stress accumulation. The present study extends our knowledge on the precise balance between lipoapoptosis and autophagy via Rubicon expression in NASH and reveals a possible pathophysiology of ballooned hepatocytes in NASH.