Basic Study
Copyright ©The Author(s) 2016. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Mar 7, 2016; 22(9): 2779-2788
Published online Mar 7, 2016. doi: 10.3748/wjg.v22.i9.2779
New role and molecular mechanism of Gadd45a in hepatic fibrosis
Liang Hong, Qing-Feng Sun, Ting-Yan Xu, Yang-He Wu, Hui Zhang, Rong-Quan Fu, Fu-Jing Cai, Qing-Qing Zhou, Ke Zhou, Qing-Wei Du, Dong Zhang, Shuang Xu, Ji-Guang Ding
Liang Hong, Qing-Feng Sun, Yang-He Wu, Hui Zhang, Rong-Quan Fu, Fu-Jing Cai, Qing-Qing Zhou, Ke Zhou, Qing-Wei Du, Dong Zhang, Shuang Xu, Ji-Guang Ding, Department of Infectious Diseases, the Third Affiliated Hospital to Wenzhou Medical University, Wenzhou 325200, Zhejiang Province, China
Ting-Yan Xu, Department of Infectious Diseases, The First Peoples Hospital of Xiaoshan Disrict, Hangzhou 311200, Zhejiang Province, China
Hui Zhang, Department of Infectious Diseases, Tianjin Baodi Hospital, Tianjin 301800, China
Author contributions: Hong L, Sun QF and Xu TY equally contributed to this paper; Hong L and Ding JG designed the research; Sun QF, Xu TY, Wu YH, Zhang H, Fu RQ, Cai FJ, Zhou QQ, Zhou K, Du QW, Zhang D and Xu S performed the research; Sun QF and Ding JG analyzed the data; and Hong L, Sun QF and Xu TY wrote the paper.
Supported by Medicine and Health Research Programs of Zhejiang Province, No. 2013KYB252; and the Science Foundation of the Science and Technology Commission of Ruian City, No. 201302012.
Institutional animal care and use committee statement: Animals (Shanghai Center of Experimental Animal, Chinese Academy of Sciences) were housed and fed with free access to food and water. All procedures were performed following approval of the Institutional Animal Care and Use Committee of the Chinese Academy of Sciences.
Conflict-of-interest statement: The authors declare no conflicts 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: http://creativecommons.org/licenses/by-nc/4.0/
Correspondence to: Ji-Guang Ding, MD, Department of Infectious Diseases, the Third Affiliated Hospital to Wenzhou Medical University, 108 Wansong Road, Wenzhou 325200, Zhejiang Province, China. djg5011@163.com
Telephone: +86-577-65866271 Fax: +86-577-65866586
Received: May 14, 2015
Peer-review started: May 15, 2015
First decision: June 19, 2015
Revised: August 4, 2015
Accepted: November 9, 2015
Article in press: November 9, 2015
Published online: March 7, 2016
Processing time: 293 Days and 2.8 Hours
Abstract

AIM: To investigate the role of Gadd45a in hepatic fibrosis and the transforming growth factor (TGF)-β/Smad signaling pathway.

METHODS: Wild-type male BALB/c mice were treated with CCl4 to induce a model of chronic liver injury. Hepatic stellate cells (HSCs) were isolated from the liver of BALB/c mice and were treated with small interfering RNAs (siRNAs) targeting Gadd45a or the pcDNA3.1-Gadd45a recombinant plasmid. Cellular α-smooth muscle actin (α-SMA), β-actin, type I collagen, phospho-Smad2, phospho-Smad3, Smad2, Smad3, and Smad4 were detected by Western blots. The mRNA levels of α-SMA, β-actin, and type I collagen were determined by quantitative real-time (qRT)-PCR analyses. Reactive oxygen species production was monitored by flow cytometry using 2,7-dichlorodihydrofluorescein diacetate. Gadd45a, Gadd45b, anti-Gadd45g, type I collagen, and SMA local expression in liver tissue were measured by histologic and immunohistochemical analyses.

RESULTS: Significant downregulation of Gadd45a, but not Gadd45b or Gadd45g, accompanied by activation of the TGF-β/Smad signaling pathways was detected in fibrotic liver tissues of mice and isolated HSCs with chronic liver injury induced by CCl4 treatment. Overexpression of Gadd45a reduced the expression of extracellular matrix proteins and α-SMA in HSCs, whereas transient knockdown of Gadd45a with siRNA reversed this process. Gadd45a inhibited the activity of a plasminogen activator inhibitor-1 promoter construct and (CAGA)9 MLP-Luc, an artificial Smad3/4-specific reporter, as well as reduced the phosphorylation and nuclear translocation of Smad3. Gadd45a showed protective effects by scavenging reactive oxygen species and upregulating antioxidant enzymes.

CONCLUSION: Gadd45a may counteract hepatic fibrosis by regulating the activation of HSCs via the inhibition of TGF-β/Smad signaling.

Keywords: Antioxidant; Gadd45a; Hepatic fibrosis; Hepatic stellate cells; Transforming growth factor-β/Smad signaling

Core tip: The data in this paper provide evidence that Gadd45a may exert a protective effect against hepatic fibrosis induced by CCl4, via the inhibition of canonical transforming growth factor-β/Smad signaling and fibrogenic gene expression. We also propose a molecular basis for the antioxidant potential of Gadd45a in the hepatic fibrosis process. Although clinical methods for the direct targeting of hepatic stellate cells remain under development, our study provides an important advance in the understanding of the biologic functions of Gadd45a and a potential target for the treatment of hepatic fibrosis.