Abstract 3112: Decrease of microRNA-122 is a key event during hepatocarcinogenesis from non-alcoholic steatohepatitis
Authors: Saito Hidetsugu , Takaki Yoko , Takasugi Azusa , Yamada Shoji , Muramatsu Toshihide , Kimura Masaki , Sugiyama Kazuo , Suzuki Hiromu , Kanai Yae , Saito Yoshimasa 
Published: August 2015

Abstract
Background and Aim: Despite improvement in the treatment of viral infection, the incidence of hepatocellular carcinoma (HCC) worldwide is still high. Non-alcoholic steatohepatitis (NASH) is a severe form of non-alcoholic fatty liver diseases and is known to develop liver cirrhosis (LC) and HCC in patients with obesity, diabetes, and metabolic syndrome. NASH may account for a large proportion of virus-independent HCC in developed countries. The aim of this study was to reveal the molecular mechanism underlying hepatocarcinogenesis from NASH, especially in the change of microRNA (miRNA) expression during carcinogenesis in an animal model. Methods and Results: MiRNA expression profiles were analyzed in STAM® mice, a NASH-HCC animal model. MicroRNA expression was also examined in 42 clinical samples from patients with HCC. Histopathology of the liver in STAM® mice at the ages of 6, 8, 12, and 18-weeks showed findings compatible with simple fatty liver, NASH, LC, and HCC, respectively. The result of miRNA expression profile showed that the liver-specific miRNA, miR-122, significantly decreased in non-tumor LC at the age of 18-weeks than that in LC at the age of 12-weeks. Expression of miR-122 was further decreased in HCCs than non-tumor LC at the age of 18-weeks. Expression of miR-122 was also decreased in clinical samples of liver tissue showing macrovesicular steatosis and HCC, being consistent with the findings in the NASH model mice. To further investigate the mechanism of decrease in miR-122 expression, the promoter region of miR-122 in human cell lines, HepG2 and HuH7, clinical samples and mice livers was analyzed. In vitro study using human cell lines revealed that the miR-122 promoter region was CpG-poor but DNA methylation of the specific region in miR-122 promoter, where peroxisome proliferator activated receptor-γ is associated, was critical for regulation of miR-122 expression, which was demonstrated by treatment with a DNA methylation inhibitor. However, the average levels of DNA methylation in the miR-122 promoter region were significantly reduced in HCC tissues than non-tumor liver tissues in human clinical samples. And also there was no significant difference in the level of DNA methylation between non-tumor LC and HCC in mice samples. These results suggested that that silencing of miR-122 was not mediated by DNA hypermethylation of the promoter region in this NASH-HCC model. Conclusion: Thus, although epigenetic regulation of miR-122 expression was still unclear, the results in the present study indicated that silencing of miR-122 was an early event during hepatocarcinogenesis from NASH, and that miR-122 could be a novel molecular marker for evaluating the risk of HCC in patients with NASH.
Citation Format: Hidetsugu Saito, Yoko Takaki, Azusa Takasugi, Shoji Yamada, Toshihide Muramatsu, Masaki Kimura, Kazuo Sugiyama, Hiromu Suzuki, Yae Kanai, Yoshimasa Saito. Decrease of microRNA-122 is a key event during hepatocarcinogenesis from non-alcoholic steatohepatitis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3112. doi:10.1158/1538-7445.AM2015-3112