MicroRNA-21 is a potential link between non-alcoholic fatty liver disease and hepatocellular carcinoma via modulation of the HBP1-p53-Srebp1c pathway

Abstract

Background Non-alcoholic fatty liver disease (NAFLD) is a major risk factor for hepatocellular carcinoma (HCC). However, the mechanistic pathways that link both disorders are essentially unknown. Objective Our study was designed to investigate the role of microRNA-21 in the pathogenesis of NAFLD and its potential involvement in HCC. Methods Wildtype mice maintained on a high fat diet (HFD) received tail vein injections of microRNA-21-anti-sense oligonucleotide (ASO) or miR-21 mismatched ASO for 4 or 8 weeks. Livers were collected after that time period for lipid content and gene expression analysis. Human hepatoma HepG2 cells incubated with oleate were used to study the role of miR-21 in lipogenesis and analysed with Nile-Red staining. microRNA-21 function in carcinogenesis was determined by soft-agar colony formation, cell cycle analysis and xenograft tumour assay using HepG2 cells. Results The expression of microRNA-21 was increased in the livers of HFD-treated mice and human HepG2 cells incubated with fatty acid. MicroRNA-21 knockdown in those mice and HepG2 cells impaired lipid accumulation and growth of xenograft tumour. Further studies revealed that Hbp1 was a novel target of microRNA-21 and a transcriptional activator of p53. It is well established that p53 is a tumour suppressor and an inhibitor of lipogenesis by inhibiting Srebp1c. As expected, microRNA-21 knockdown led to increased HBP1 and p53 and subsequently reduced lipogenesis and delayed G1/S transition, and the additional treatment of HBP1-siRNA antagonised the effect of microRNA-21-ASO, suggesting that HBP1 mediated the inhibitory effects of microRNA-21-ASO on both hepatic lipid accumulation and hepatocarcinogenesis. Mechanistically, microRNA-21 knockdown induced p53 transcription, which subsequently reduced expression of genes controlling lipogenesis and cell cycle transition. In contrast, the opposite result was observed with overexpression of microRNA-21, which prevented p53 transcription. Conclusions Our findings reveal a novel mechanism by which microRNA-21, in part, promotes hepatic lipid accumulation and cancer progression by interacting with the Hbp1-p53-Srebp1c pathway and suggest the potential therapeutic value of microRNA-21-ASO for both disorders.

Stress-activatedmiR-21/miR-21*in hepatocytes promotes lipid and glucose metabolic disorders associated with high-fat diet consumption

“…miR-21 is a highly expressed miRNA in the liver42 and is further upregulated with obesity,30–32 43 44 steatohepatitis and fibrosis,18 31 as well as in cholangiocarcinoma and HCC 21 22. Actually, hundreds of miRNAs have been shown to be deregulated in human NAFLD, steatohepatitis and diabetes, each of them potentially controlling different and multiple aspects of hepatocyte biology, such as insulin sensitivity, lipid and glucose metabolism, endoplasmic reticulum and oxidative stresses, cell apoptosis and survival 45–47.…”

“…While preparing this manuscript, we also became aware of a study by Wu et al, 44 who described a mechanism involving a HBP1-P53-SREBP1C pathway in the control of diet-induced steatosis development by miR-21 . To this end, they used synthetic inhibitors of miR-21 in vivo in mice and in vitro in HepG2-cultured cells 44.…”

Emerging role of miR-21 in non-alcoholic fatty liver disease

“…The increased expression of p53, a known inhibitor of SREPB1-c and a target of miR-21, indeed suggests an alternative pathway for the regulation of SREBP-1c mediated lipogenesis. However, the effect on SREBP-1c seemed independent of the transcription factor HBP1 (HMG-box transcription factor 1), recently shown to be part of the p53/SREBP-1c signalling pathway 6. A slight decrease in FAT/CD36 (fatty acid translocase) and FATP1 (fatty acid transport protein 1) was observed in parallel, suggesting a potential reduction in fatty acid uptake.…”

A decrease in hepatic microRNA-9 expression impairs gluconeogenesis by targeting FOXO1 in obese mice

“…Deletion of hepatic miR-9 leads to an increase of fasting blood glucose levels in lean mice We further investigated whether hepatic miR-9 affects insulin sensitivity by injecting an miR-9 inhibitor into C57BL/6J mice via the tail vein, as previously described [29]. Figure 6a shows that the miR-9 inhibitor significantly decreased miR-9 expression in hepatocytes.…”

“…Mice were injected i.v. through the tail vein with a lipid nanoparticle-formulated miR-9 inhibitor or miR-9 mimic, at a dose of 100 nmol in 0.2 ml PBS, as described previously [29]. The DNA methyltransferase (DNMT) inhibitor was injected into ob/+ or ob/ob mice as described previously [30].…”